Collections

What Is a Collection?

A collection is an ordered group of elements, all of the same type. It is a general concept that encompasses lists, arrays, and other datatypes used in classic programming algorithms. Each element is addressed by a unique subscript.
PL/SQL offers these collection types:

• Associative arrays, also known as index-by tables, let you look up elements using arbitrary numbers and strings for subscript values. (They are similar to hash tables in other programming languages.)
• Nested tables hold an arbitrary number of elements. They use sequential numbers as subscripts. You can define equivalent SQL types, allowing nested tables to be stored in database tables and manipulated through SQL.
• Varrays (short for variable-size arrays) hold a fixed number of elements (although you can change the number of elements at runtime). They use sequential numbers as subscripts. You can define equivalent SQL types, allowing varrays to be stored in database tables. They can be stored and retrieved through SQL, but with less flexibility than nested tables.

Although collections have only one dimension, you can model multi-dimensional arrays by creating collections whose elements are also collections.
To use collections in an application, you define one or more PL/SQL types, then define variables of those types. You can define collection types in a procedure, function, or package. You can pass collection variables as parameters to stored subprograms.
To look up data that is more complex than single values, you can store PL/SQL records or SQL object types in collections. Nested tables and varrays can also be attributes of object types.

Understanding Nested Tables

PL/SQL nested tables represent sets of values. You can think of them as one-dimensional arrays with no upper bound. You can model multi-dimensional arrays by creating nested tables whose elements are also nested tables.
Within the database, nested tables are column types that hold sets of values. Oracle stores the rows of a nested table in no particular order. When you retrieve a nested table from the database into a PL/SQL variable, the rows are given consecutive subscripts starting at 1. That gives you array-like access to individual rows.
Nested tables differ from arrays in two important ways:

1. Nested tables are unbounded, while arrays have a fixed upper bound (see Figure 5-1). The size of a nested table can increase dynamically.
2. Nested tables might not have consecutive subscripts, while arrays are always dense (have consecutive subscripts). Initially, nested tables are dense, but they can become sparse (have nonconsecutive subscripts). You can delete elements from a nested table using the built-in procedure DELETE. The built-in function NEXT lets you iterate over all the subscripts of a nested table, even if the sequence has gaps.

Figure 5-1 Array versus Nested Table

Description of the illustration lnpls016.gif

Understanding Varrays

Items of type VARRAY are called varrays. They let you reference individual elements for array operations, or manipulate the collection as a whole. To reference an element, you use standard subscripting syntax (see Figure 5-2). For example, Grade(3) references the third element in varray Grades.

Figure 5-2 Varray of Size 10

Description of the illustration lnpls017.gif

A varray has a maximum size, which you specify in its type definition. Its index has a fixed lower bound of 1 and an extensible upper bound. For example, the current upper bound for varray Grades is 7, but you can increase its upper bound to maximum of 10. A varray can contain a varying number of elements, from zero (when empty) to the maximum specified in its type definition.

Understanding Associative Arrays (Index-By Tables)

Associative arrays are sets of key-value pairs, where each key is unique and is used to locate a corresponding value in the array. The key can be an integer or a string.
Assigning a value using a key for the first time adds that key to the associative array. Subsequent assignments using the same key update the same entry. It is important to choose a key that is unique. For example, key values might come from the primary key of a database table, from a numeric hash function, or from concatenating strings to form a unique string value.
For example, here is the declaration of an associative array type, and two arrays of that type, using keys that are strings:

DECLARE
  TYPE population_type IS TABLE OF NUMBER INDEX BY VARCHAR2(64);
  country_population population_type;
  continent_population population_type;
  howmany NUMBER;
  which VARCHAR2(64);
BEGIN
  country_population('Greenland') := 100000; -- Creates new entry
  country_population('Iceland') := 750000;   -- Creates new entry
-- Looks up value associated with a string
  howmany := country_population('Greenland');

  continent_population('Australia') := 30000000;
  continent_population('Antarctica') := 1000; -- Creates new entry
  continent_population('Antarctica') := 1001; -- Replaces previous value 

-- Returns 'Antarctica' as that comes first alphabetically.
  which := continent_population.FIRST;
-- Returns 'Australia' as that comes last alphabetically.
  which := continent_population.LAST;
-- Returns the value corresponding to the last key, in this
-- case the population of Australia.
  howmany := continent_population(continent_population.LAST);
END;
/

Associative arrays help you represent data sets of arbitrary size, with fast lookup for an individual element without knowing its position within the array and without having to loop through all the array elements. It is like a simple version of a SQL table where you can retrieve values based on the primary key. For simple temporary storage of lookup data, associative arrays let you avoid using the disk space and network operations required for SQL tables.
Because associative arrays are intended for temporary data rather than storing persistent data, you cannot use them with SQL statements such as INSERT and SELECT INTO. You can make them persistent for the life of a database session by declaring the type in a package and assigning the values in a package body.

How Globalization Settings Affect VARCHAR2 Keys for Associative Arrays

If settings for national language or globalization change during a session that uses associative arrays with VARCHAR2 key values, the program might encounter a runtime error. For example, changing the NLS_COMP or NLS_SORT initialization parameters within a session might cause methods such as NEXT and PRIOR to raise exceptions. If you need to change these settings during the session, make sure to set them back to their original values before performing further operations with these kinds of associative arrays.
When you declare an associative array using a string as the key, the declaration must use a VARCHAR2, STRING, or LONG type. You can use a different type, such as NCHAR or NVARCHAR2, as the key value to reference an associative array. You can even use a type such as DATE, as long as it can be converted to VARCHAR2 by the TO_CHAR function.
However, you must be careful when using other types that the values used as keys are consistent and unique. For example, the string value of SYSDATE might change if the NLS_DATE_FORMAT initialization parameter changes, so that array_element(SYSDATE) does not produce the same result as before. Two different NVARCHAR2 values might turn into the same VARCHAR2 value (containing question marks instead of certain national characters). In that case, array_element(national_string1) and array_element(national_string2) might refer to the same element. Two different CHAR or VARCHAR2 values that differ in terms of case, accented characters, or punctuation characters might also be considered the same if the value of the NLS_SORT initialization parameter ends in _CI (case-insensitive comparisons) or _AI (accent- and case-insensitive comparisons).
When you pass an associative array as a parameter to a remote database using a database link, the two databases can have different globalization settings. When the remote database performs operations such as FIRST and NEXT, it uses its own character order even if that is different from the order where the collection originated. If character set differences mean that two keys that were unique are not unique on the remote database, the program receives a VALUE_ERROR exception.

Choosing Which PL/SQL Collection Types to Use

If you already have code or business logic that uses some other language, you can usually translate that language's array and set types directly to PL/SQL collection types.

• Arrays in other languages become varrays in PL/SQL.
• Sets and bags in other languages become nested tables in PL/SQL.
• Hash tables and other kinds of unordered lookup tables in other languages become associative arrays in PL/SQL.

When you are writing original code or designing the business logic from the start, you should consider the strengths of each collection type to decide which is appropriate for each situation.

Choosing Between Nested Tables and Associative Arrays

Both nested tables and associative arrays (formerly known as index-by tables) use similar subscript notation, but they have different characteristics when it comes to persistence and ease of parameter passing.
Nested tables can be stored in a database column, but associative arrays cannot. Nested tables can simplify SQL operations where you would normally join a single-column table with a larger table.
Associative arrays are appropriate for relatively small lookup tables where the collection can be constructed in memory each time a procedure is called or a package is initialized. They are good for collecting information whose volume is unknown beforehand, because there is no fixed limit on their size. Their index values are more flexible, because associative array subscripts can be negative, can be nonsequential, and can use string values instead of numbers.
PL/SQL automatically converts between host arrays and associative arrays that use numeric key values. The most efficient way to pass collections to and from the database server is to set up data values in associative arrays, then use those associative arrays with bulk constructs (the FORALL statement or BULK COLLECT clause).

Choosing Between Nested Tables and Varrays

Varrays are a good choice when:

• The number of elements is known in advance.
• The elements are usually all accessed in sequence.

When stored in the database, varrays keep their ordering and subscripts.
Each varray is stored as a single object, either inside the table of which it is a column (if the varray is less than 4KB) or outside the table but still in the same tablespace (if the varray is greater than 4KB). You must update or retrieve all elements of the varray at the same time, which is most appropriate when performing some operation on all the elements at once. But you might find it impractical to store and retrieve large numbers of elements this way.
Nested tables are a good choice when:

• The index values are not consecutive.
• There is no predefined upper bound for index values.
• You need to delete or update some elements, but not all the elements at once.
• You would usually create a separate lookup table, with multiple entries for each row of the main table, and access it through join queries.

Nested tables can be sparse: you can delete arbitrary elements, rather than just removing an item from the end.
Nested table data is stored in a separate store table, a system-generated database table associated with the nested table. The database joins the tables for you when you access the nested table. This makes nested tables suitable for queries and updates that only affect some elements of the collection.
You cannot rely on the order and subscripts of a nested table remaining stable as the nested table is stored in and retrieved from the database, because the order and subscripts are not preserved in the database.

Defining Collection Types

To create collections, you define a collection type, then declare variables of that type. You can define TABLE and VARRAY types in the declarative part of any PL/SQL block, subprogram, or package.
Collections follow the same scoping and instantiation rules as other types and variables. Collections are instantiated when you enter a block or subprogram, and cease to exist when you exit. In a package, collections are instantiated when you first reference the package and cease to exist when you end the database session.

Nested Tables
To define a PL/SQL type for nested tables, use the syntax:

TYPE type_name IS TABLE OF element_type [NOT NULL];

type_name is a type specifier used later to declare collections. For nested tables declared within PL/SQL, element_type is any PL/SQL datatype except:

REF CURSOR

Nested tables declared in SQL using the CREATE TYPE statement have additional restrictions on the element type. They cannot use the following element types:

BINARY_INTEGER, PLS_INTEGER

BOOLEAN

LONG, LONG RAW

NATURAL, NATURALN

POSITIVE, POSITIVEN

REF CURSOR

SIGNTYPE

STRING

Varrays
To define a PL/SQL type for varrays, use the syntax:

TYPE type_name IS {VARRAY | VARYING ARRAY} (size_limit) 
   OF element_type [NOT NULL];

The meanings of type_name and element_type are the same as for nested tables.
size_limit is a positive integer literal representing the maximum number of elements in the array.
When defining a VARRAY type, you must specify its maximum size. In the following example, you define a type that stores up to 366 dates:

DECLARE
   TYPE Calendar IS VARRAY(366) OF DATE;
BEGIN
   NULL;
END;
/

Associative Arrays
Associative arrays (also known as index-by tables) let you insert elements using arbitrary key values. The keys do not have to be consecutive. They use the syntax:

TYPE type_name IS TABLE OF element_type [NOT NULL]
   INDEX BY [PLS_INTEGER | BINARY_INTEGER | VARCHAR2(size_limit)];
   INDEX BY key_type;

The key_type can be numeric, either PLS_INTEGER or BINARY_INTEGER. It can also be VARCHAR2 or one of its subtypes VARCHAR, STRING, or LONG. You must specify the length of a VARCHAR2-based key, except for LONG which is equivalent to declaring a key type of VARCHAR2(32760). The types RAW, LONG RAW, ROWID, CHAR, and CHARACTER are not allowed as keys for an associative array.
An initialization clause is not allowed. There is no constructor notation for associative arrays.
When you reference an element of an associative array that uses a VARCHAR2-based key, you can use other types, such as DATE or TIMESTAMP, as long as they can be converted to VARCHAR2 with the TO_CHAR function.
Associative arrays can store data using a primary key value as the index, where the key values are not sequential. The example below creates a single element in an associative array, with a subscript of 100 rather than 1:

DECLARE
   TYPE EmpTabTyp IS TABLE OF employees%ROWTYPE
      INDEX BY PLS_INTEGER;
   emp_tab EmpTabTyp;
BEGIN
   /* Retrieve employee record. */
   SELECT * INTO emp_tab(100) FROM employees WHERE employee_id = 100;
END;
/

Defining SQL Types Equivalent to PL/SQL Collection Types

To store nested tables and varrays inside database tables, you must also declare SQL types using the CREATE TYPE statement. The SQL types can be used as columns or as attributes of SQL object types.
You can declare equivalent types within PL/SQL, or use the SQL type name in a PL/SQL variable declaration.

Example 5-1 Declaring a Nested Table in SQL
The following SQL*Plus script shows how you might declare a nested table in SQL, and use it as an attribute of an object type:

CREATE TYPE CourseList AS TABLE OF VARCHAR2(10)  -- define type
/
CREATE TYPE Student AS OBJECT (  -- create object
   id_num  INTEGER(4),
   name    VARCHAR2(25),
   address VARCHAR2(35),
   status  CHAR(2),
   courses CourseList);  -- declare nested table as attribute
/

DROP TYPE Student;
DROP TYPE CourseList;

The identifier courses represents an entire nested table. Each element of courses stores the name of a college course such as 'Math 1020'.

Example 5-2 Creating a Table with a Varray Column
The script below creates a database column that stores varrays. Each varray element contains a VARCHAR2.

-- Each project has a 16-character code name.
-- We will store up to 50 projects at a time in a database column.
CREATE TYPE ProjectList AS VARRAY(50) OF VARCHAR2(16);
/
CREATE TABLE department (  -- create database table
   dept_id  NUMBER(2),
   name     VARCHAR2(15),
   budget   NUMBER(11,2),
-- Each department can have up to 50 projects.
   projects ProjectList);

DROP TABLE department;
DROP TYPE ProjectList;

Declaring PL/SQL Collection Variables

After defining a collection type, you declare variables of that type. You use the new type name in the declaration, the same as with predefined types such as NUMBER.

Example 5-3 Declaring Nested Tables, Varrays, and Associative Arrays

DECLARE
   TYPE nested_type IS TABLE OF VARCHAR2(20);
   TYPE varray_type IS VARRAY(5) OF INTEGER;
   TYPE assoc_array_num_type IS TABLE OF NUMBER INDEX BY PLS_INTEGER;
   TYPE assoc_array_str_type IS TABLE OF VARCHAR2(32) INDEX BY PLS_INTEGER;
   TYPE assoc_array_str_type2 IS TABLE OF VARCHAR2(32) INDEX BY VARCHAR2(64);
   v1 nested_type;
   v2 varray_type;
   v3 assoc_array_num_type;
   v4 assoc_array_str_type;
   v5 assoc_array_str_type2;
BEGIN
   v1 := nested_type('Arbitrary','number','of','strings');
   v2 := varray_type(10, 20, 40, 80, 160); -- Up to 5 integers
   v3(99) := 10; -- Just start assigning to elements.
   v3(7) := 100; -- Subscripts can be any integer values.
   v4(42) := 'Cat'; -- Just start assigning to elements.
   v4(54) := 'Hat'; -- Subscripts can be any integer values.
   v5('Canada') := 'North America'; -- Just start assigning to elements.
   v5('Greece') := 'Europe';        -- Subscripts can be string values.
END;
/

Example 5-4 Declaring Collections with %TYPE
You can use %TYPE to specify the datatype of a previously declared collection, so that changing the definition of the collection automatically updates other variables that depend on the number of elements or the element type:

DECLARE
   TYPE Few_Colors IS VARRAY(10) OF VARCHAR2(20);
   TYPE Many_Colors IS VARRAY(100) OF VARCHAR2(64);
   some_colors Few_Colors;
-- If we change the type of SOME_COLORS from FEW_COLORS to MANY_COLORS,
-- RAINBOW and CRAYONS will use the same type when this block is recompiled.
   rainbow some_colors%TYPE;
   crayons some_colors%TYPE;
BEGIN
   NULL;
END;
/

Example 5-5 Declaring a Procedure Parameter as a Nested Table
You can declare collections as the formal parameters of functions and procedures. That way, you can pass collections to stored subprograms and from one subprogram to another. The following example declares a nested table as a parameter of a packaged procedure:

CREATE PACKAGE personnel AS
   TYPE Staff_List IS TABLE OF employees.employee_id%TYPE;
   PROCEDURE award_bonuses (who_gets_em IN Staff_List);
END personnel;
/

DROP PACKAGE personnel;

To call PERSONNEL.AWARD_BONUSES from outside the package, you declare a variable of type PERSONNEL.STAFF and pass that variable as the parameter.
You can also specify a collection type in the RETURN clause of a function specification.

Example 5-6 Specifying Collection Element Types with %TYPE and %ROWTYPE
To specify the element type, you can use %TYPE, which provides the datatype of a variable or database column. Also, you can use %ROWTYPE, which provides the rowtype of a cursor or database table. Two examples follow:

DECLARE
-- Nested table type that can hold an arbitrary number of
-- employee IDs. The element type is based on a column from
-- the EMPLOYEES table. We do not need to know whether the
-- ID is a number or a string.
   TYPE EmpList IS TABLE OF employees.employee_id%TYPE;

-- Array type that can hold information about 10 employees.
-- The element type is a record that contains all the same
-- fields as the EMPLOYEES table.
   TYPE Top_Salespeople IS VARRAY(10) OF employees%ROWTYPE;

-- Declare a cursor to select a subset of columns.
   CURSOR c1 IS SELECT first_name, last_name FROM employees;
-- Array type that can hold a list of names. The element type
-- is a record that contains the same fields as the cursor
-- (that is, first_name and last_name).
   TYPE NameList IS VARRAY(20) OF c1%ROWTYPE;
BEGIN
   NULL;
END;
/

Example 5-7 VARRAY of Records
This example uses a RECORD type to specify the element type:

DECLARE
   TYPE GlossEntry IS RECORD ( term VARCHAR2(20), meaning VARCHAR2(200) ); 
   TYPE Glossary IS VARRAY(250) OF GlossEntry;
BEGIN
   NULL;
END;
/

Example 5-8 NOT NULL Constraint on Collection Elements
You can also impose a NOT NULL constraint on the element type:

DECLARE
   TYPE EmpList IS TABLE OF employees.employee_id%TYPE NOT NULL;
   my_employees EmpList := EmpList(100, 150, 160, 200);
BEGIN
   my_employees(3) := NULL; -- Assigning NULL raises an exception
END;
/

Initializing and Referencing Collections

Until you initialize it, a nested table or varray is atomically null: the collection itself is null, not its elements. To initialize a nested table or varray, you use a constructor, a system-defined function with the same name as the collection type. This function "constructs" collections from the elements passed to it.
You must explicitly call a constructor for each varray and nested table variable. (Associative arrays, the third kind of collection, do not use constructors.) Constructor calls are allowed wherever function calls are allowed.

Example 5-9 Constructor for a Nested Table
The following example initializes a nested table using a constructor, which looks like a function with the same name as the collection type:

DECLARE
   TYPE Colors IS TABLE OF VARCHAR2(16);
   rainbow Colors;
BEGIN
   rainbow := Colors('Red','Orange','Yellow','Green','Blue','Indigo','Violet');
END;
/

Because a nested table does not have a declared maximum size, you can put as many elements in the constructor as necessary.

Example 5-10 Constructor for a Varray
This example initializes a varray using a constructor, which looks like a function with the same name as the collection type:

DECLARE
-- In the varray, we put an upper limit on the number of elements.
   TYPE Colors IS VARRAY(10) OF VARCHAR2(16);
   rainbow Colors;
BEGIN
-- Since COLORS is declared as VARRAY(10), we can put up to 10
-- elements in the constructor.
   rainbow := Colors('Red','Orange','Yellow','Green','Blue','Indigo','Violet');
END;
/

Example 5-11 Collection Constructor Including Null Elements
Unless you impose the NOT NULL constraint in the type declaration, you can pass null elements to a constructor:

DECLARE
   TYPE Colors IS TABLE OF VARCHAR2(20);
   my_colors Colors;
   TYPE ColorsNoNulls IS TABLE OF VARCHAR2(20) NOT NULL;
BEGIN
   my_colors := Colors('Sienna',NULL,'Teal','Umber',NULL);
-- If MY_COLORS was of type ColorsNoNulls, we could not include
-- null values in the constructor.
END;
/

Example 5-12 Combining Collection Declaration and Constructor
You can initialize a collection in its declaration, which is a good programming practice:

DECLARE
   TYPE Colors IS TABLE OF VARCHAR2(20);
   my_colors Colors := Colors('Brown','Gray','Beige');
BEGIN
   NULL;
END;
/

Example 5-13 Empty Varray Constructor
If you call a constructor without arguments, you get an empty but non-null collection:

DECLARE
   TYPE Colors IS VARRAY(100) OF VARCHAR2(20);
   my_colors Colors;
BEGIN
   IF my_colors IS NULL THEN
      dbms_output.put_line('Before initialization, the varray is null.');
-- While the varray is null, we can't check its COUNT attribute.
--      dbms_output.put_line('It has ' || my_colors.COUNT || ' elements.');
   ELSE
      dbms_output.put_line('Before initialization, the varray is not null.');
   END IF;
   my_colors := Colors(); -- initialize empty varray 
   IF my_colors IS NULL THEN
      dbms_output.put_line('After initialization, the varray is null.');
   ELSE
      dbms_output.put_line('After initialization, the varray is not null.');
      dbms_output.put_line('It has ' || my_colors.COUNT || ' elements.');
   END IF;
END;
/

In this case, you can call the collection's EXTEND method to add elements later.

Example 5-14 Nested Table Constructor Within a SQL Statement
In this example, you insert several scalar values and a CourseList nested table into the SOPHOMORES table.

BEGIN
   INSERT INTO sophomores
      VALUES (5035, 'Janet Alvarez', '122 Broad St', 'FT',
         CourseList('Econ 2010', 'Acct 3401', 'Mgmt 3100'));

Example 5-15 Varray Constructor Within a SQL Statement
In this example, you insert a row into database table DEPARTMENT. The varray constructor ProjectList() provides a value for column PROJECTS.

BEGIN
  INSERT INTO department
    VALUES(60, 'Security', 750400,
      ProjectList('New Badges', 'Track Computers', 'Check Exits'));

Referencing Collection Elements

Every reference to an element includes a collection name and a subscript enclosed in parentheses. The subscript determines which element is processed. To reference an element, you specify its subscript using the syntax

collection_name(subscript)

where subscript is an expression that yields an integer in most cases, or a VARCHAR2 for associative arrays declared with strings as keys.
The allowed subscript ranges are:

• For nested tables, 1 .. 2**31.
• For varrays, 1 ..  size_limit, where you specify the limit in the declaration.
• For associative arrays with a numeric key, -2**31 .. 2**31.
• For associative arrays with a string key, the length of the key and number of possible values depends on the VARCHAR2 length limit in the type declaration, and the database character set.

Example 5-16 Referencing a Nested Table Element By Subscript
This example shows how to reference an element in the nested table NAMES:

DECLARE
   TYPE Roster IS TABLE OF VARCHAR2(15);
   names Roster := Roster('J Hamil', 'D Caruso', 'R Singh');
BEGIN
  FOR i IN names.FIRST .. names.LAST
  LOOP
      IF names(i) = 'J Hamil' THEN
        NULL;
      END IF;
  END LOOP;
END;
/

Example 5-17 Passing a Nested Table Element as a Parameter
This example shows that you can reference the elements of a collection in subprogram calls:

DECLARE
   TYPE Roster IS TABLE OF VARCHAR2(15);
   names Roster := Roster('J Hamil', 'D Piro', 'R Singh');
   i BINARY_INTEGER := 2;
BEGIN
   verify_name(names(i));  -- call procedure
END;
/

Assigning Collections

One collection can be assigned to another by an INSERT, UPDATE, FETCH, or SELECT statement, an assignment statement, or a subprogram call.
You can assign the value of an expression to a specific element in a collection using the syntax:

collection_name(subscript) := expression;

where expression yields a value of the type specified for elements in the collection type definition.
You can use operators such as SET, MULTISET UNION, MULTISET INTERSECT, and MULTISET EXCEPT to transform nested tables as part of an assignment statement.

Example 5-18 Datatype Compatibility for Collection Assignment
This example shows that collections must have the same datatype for an assignment to work. Having the same element type is not enough.

DECLARE
   TYPE last_name_typ IS VARRAY(3) OF VARCHAR2(64);
   TYPE surname_typ IS VARRAY(3) OF VARCHAR2(64);
-- These first two variables have the same datatype.
   group1 last_name_typ := last_name_typ('Jones','Wong','Marceau');
   group2 last_name_typ := last_name_typ('Klein','Patsos','Singh');
-- This third variable has a similar declaration, but is not the same type.
   group3 surname_typ := surname_typ('Trevisi','Macleod','Marquez');
BEGIN
-- Allowed because they have the same datatype
   group1 := group2;
-- Not allowed because they have different datatypes
--   group3 := group2;
END;
/

Example 5-19 Assigning a Null Value to a Nested Table
If you assign an atomically null nested table or varray to a second nested table or varray, the second collection must be reinitialized:

DECLARE
   TYPE Colors IS TABLE OF VARCHAR2(64);
-- This nested table has some values.
   crayons Colors := Colors('Silver','Gold');
-- This nested table is not initialized ("atomically null").
   empty_set Colors;
BEGIN
-- At first, the initialized variable is not null.
   if crayons IS NOT NULL THEN
      dbms_output.put_line('OK, at first crayons is not null.');
   END IF;

-- Then we assign a null nested table to it.
   crayons := empty_set;

-- Now it is null.
   if crayons IS NULL THEN
      dbms_output.put_line('OK, now crayons has become null.');
   END IF;

-- We must use another constructor to give it some values.
   crayons := Colors('Yellow','Green','Blue');
END;
/

In the same way, assigning the value NULL to a collection makes it atomically null.

Example 5-20 Possible Exceptions for Collection Assignments
Assigning a value to a collection element can cause various exceptions:

• If the subscript is null or is not convertible to the right datatype, PL/SQL raises the predefined exception VALUE_ERROR. Usually, the subscript must be an integer. Associative arrays can also be declared to have VARCHAR2 subscripts.
• If the subscript refers to an uninitialized element, PL/SQL raises SUBSCRIPT_BEYOND_COUNT.
• If the collection is atomically null, PL/SQL raises COLLECTION_IS_NULL.

DECLARE
   TYPE WordList IS TABLE OF VARCHAR2(5);
   words WordList;
BEGIN
   /* Assume execution continues despite the raised exceptions. */
-- Raises COLLECTION_IS_NULL. We haven't used a constructor yet.
-- This exception applies to varrays and nested tables, but not to
-- associative arrays which don't need a constructor.
   words(1) := 10;
-- After using a constructor, we can assign values to the elements.
   words := WordList(10,20,30);
-- Any expression that returns a VARCHAR2(5) is OK.
   words(1) := 'yes';
   words(2) := words(1) || 'no';
-- Raises VALUE_ERROR because the assigned value is too long.
   words(3) := 'longer than 5 characters';
-- Raises VALUE_ERROR because the subscript of a nested table must
-- be an integer.
   words('B') := 'dunno';
-- Raises SUBSCRIPT_BEYOND_COUNT because we only made 3 elements
-- in the constructor. To add new ones, we must call the EXTEND
-- method first.
   words(4) := 'maybe';
END;
/

Example 5-21 Assigning Nested Tables with Set Operators
This example shows some of the ANSI-standard operators that you can apply to nested tables:

DECLARE
  TYPE nested_typ IS TABLE OF NUMBER;
  nt1 nested_typ := nested_typ(1,2,3);
  nt2 nested_typ := nested_typ(3,2,1);
  nt3 nested_typ := nested_typ(2,3,1,3);
  nt4 nested_typ := nested_typ(1,2,4);
  answer nested_typ;

-- The results might be in a different order than you expect.
-- (Remember, you should not rely on the order of elements in nested tables.)
  PROCEDURE print_nested_table(the_nt nested_typ) IS
     output VARCHAR2(128);
  BEGIN
     IF the_nt IS NULL THEN
        dbms_output.put_line('Results: <NULL>');
        RETURN;
     END IF;
     IF the_nt.COUNT = 0 THEN
        dbms_output.put_line('Results: empty set');
        RETURN;
     END IF;
     FOR i IN the_nt.FIRST .. the_nt.LAST
     LOOP
        output := output || the_nt(i) || ' ';
     END LOOP;
     dbms_output.put_line('Results: ' || output);
  END;
BEGIN
  answer := nt1 MULTISET UNION nt4; -- (1,2,3,1,2,4)
  print_nested_table(answer);
  answer := nt1 MULTISET UNION nt3; -- (1,2,3,2,3,1,3)
  print_nested_table(answer);
  answer := nt1 MULTISET UNION DISTINCT nt3; -- (1,2,3)
  print_nested_table(answer);

  answer := nt2 MULTISET INTERSECT nt3; -- (3,2,1)
  print_nested_table(answer);
  answer := nt2 MULTISET INTERSECT DISTINCT nt3; -- (3,2,1)
  print_nested_table(answer);

  answer := SET(nt3); -- (2,3,1)
  print_nested_table(answer);

  answer := nt3 MULTISET EXCEPT nt2; -- (3)
  print_nested_table(answer);
  answer := nt3 MULTISET EXCEPT DISTINCT nt2; -- ()
  print_nested_table(answer);

END;
/

Comparing Collections

You can check whether a collection is null, and whether two collections are the same. Comparisons such as greater than, less than, and so on are not allowed.
This restriction also applies to implicit comparisons. For example, collections cannot appear in a DISTINCT, GROUP BY, or ORDER BY list.
If you want to do such comparison operations, you must define your own notion of what it means for collections to be greater than, less than, and so on, and write one or more functions to examine the collections and their elements and return a true or false value.
You can apply set operators (CARDINALITY, MEMBER OF, IS A SET, IS EMPTY) to check certain conditions within a nested table or between two nested tables.

Example 5-22 Checking if a Collection Is Null
Nested tables and varrays can be atomically null, so they can be tested for nullity:

DECLARE
   TYPE Staff IS TABLE OF Employee;
   members Staff;
BEGIN
  -- Condition yields TRUE because we haven't used a constructor.
   IF members IS NULL THEN ...
END;

Example 5-23 Comparing Two Collections
Collections can be compared for equality or inequality. They cannot be ordered, because there is no "greater than" or "less than" comparison.

DECLARE
   TYPE Colors IS TABLE OF VARCHAR2(64);
   primaries Colors := Colors('Blue','Green','Red');
   rgb Colors := Colors('Red','Green','Blue');
   traffic_light Colors := Colors('Red','Green','Amber');
BEGIN
-- We can use = or !=, but not < or >.
-- Notice that these 2 are equal even though the members are in different order.
   IF primaries = rgb THEN
      dbms_output.put_line('OK, PRIMARIES and RGB have the same members.');
   END IF;
   IF rgb != traffic_light THEN
      dbms_output.put_line('OK, RGB and TRAFFIC_LIGHT have different members.');
   END IF;
END;
/

Example 5-24 Comparing Nested Tables with Set Operators
You can test certain properties of a nested table, or compare two nested tables, using ANSI-standard set operations:

DECLARE
  TYPE nested_typ IS TABLE OF NUMBER;
  nt1 nested_typ := nested_typ(1,2,3);
  nt2 nested_typ := nested_typ(3,2,1);
  nt3 nested_typ := nested_typ(2,3,1,3);
  nt4 nested_typ := nested_typ(1,2,4);
  answer BOOLEAN;
  howmany NUMBER;
  PROCEDURE testify(truth BOOLEAN DEFAULT NULL, quantity NUMBER DEFAULT NULL) IS
  BEGIN
     IF truth IS NOT NULL THEN
        dbms_output.put_line(CASE truth WHEN TRUE THEN 'True' WHEN FALSE THEN 'False' END);
     END IF;
     IF quantity IS NOT NULL THEN
        dbms_output.put_line(quantity);
     END IF;
  END;
BEGIN
  answer := nt1 IN (nt2,nt3,nt4); -- true, nt1 matches nt2
  testify(truth => answer);
  answer := nt1 SUBMULTISET OF nt3; -- true, all elements match
  testify(truth => answer);
  answer := nt1 NOT SUBMULTISET OF nt4; -- also true
  testify(truth => answer);

  howmany := CARDINALITY(nt3); -- number of elements in nt3
  testify(quantity => howmany);
  howmany := CARDINALITY(SET(nt3)); -- number of distinct elements
  testify(quantity => howmany);

  answer := 4 MEMBER OF nt1; -- false, no element matches
  testify(truth => answer);
  answer := nt3 IS A SET; -- false, nt3 has duplicates
  testify(truth => answer);
  answer := nt3 IS NOT A SET; -- true, nt3 has duplicates
  testify(truth => answer);
  answer := nt1 IS EMPTY; -- false, nt1 has some members
  testify(truth => answer);
END;
/

Using PL/SQL Collections with SQL Statements

Collections let you manipulate complex datatypes within PL/SQL. Your program can compute subscripts to process specific elements in memory, and use SQL to store the results in database tables.

Example 5-25 Creating a SQL Type Corresponding to a PL/SQL Nested Table
In SQL*Plus, you can create SQL types whose definitions correspond to PL/SQL nested tables and varrays:

SQL> CREATE TYPE CourseList AS TABLE OF VARCHAR2(64);

You can use these SQL types as columns in database tables:

SQL> CREATE TABLE department (
  2  name     VARCHAR2(20),
  3  director VARCHAR2(20),
  4  office   VARCHAR2(20),
  5  courses  CourseList) 
  6  NESTED TABLE courses STORE AS courses_tab;

Each item in column COURSES is a nested table that will store the courses offered by a given department. The NESTED TABLE clause is required whenever a database table has a nested table column. The clause identifies the nested table and names a system-generated store table, in which Oracle stores the nested table data.

Example 5-26 Inserting a Nested Table into a Database Table
Now, you can populate the database table. The table constructor provides values that all go into the single column COURSES:

BEGIN
   INSERT INTO department
      VALUES('English', 'Lynn Saunders', 'Breakstone Hall 205',
         CourseList('Expository Writing',
                    'Film and Literature',
                    'Modern Science Fiction',
                    'Discursive Writing',
                    'Modern English Grammar',
                    'Introduction to Shakespeare',
                    'Modern Drama',
                    'The Short Story',
                    'The American Novel'));
END;

Example 5-27 Using PL/SQL Nested Tables with INSERT, UPDATE, DELETE, and SELECT Statements
You can retrieve all the courses offered by the English department into a PL/SQL nested table:

CREATE TYPE ColorList AS TABLE OF VARCHAR2(64);
/
CREATE TABLE flowers (name VARCHAR2(20), colors ColorList) NESTED TABLE colors STORE AS colors_tab;

BEGIN
   INSERT INTO flowers VALUES('Rose', ColorList('Red','Yellow','White'));
   INSERT INTO flowers VALUES('Tulip', ColorList('Red','White','Yellow', 'Blue'));
   INSERT INTO flowers VALUES('Iris', ColorList('White','Purple'));
   COMMIT;
END;
/

DECLARE
-- This type declaration is not needed, because PL/SQL can see the SQL type.
--   TYPE ColorList IS TABLE OF VARCHAR2(64);
-- Declare a variable that can hold a set of colors.
   my_colors ColorList;
-- Declare a record that can hold a row from the table.
-- One of the record fields is a set of colors.
   my_flower flowers%ROWTYPE;
   new_colors ColorList;
BEGIN
-- Look up a name and query just the associated colors.
   SELECT colors INTO my_colors FROM flowers WHERE name = 'Rose';
   FOR i IN my_colors.FIRST .. my_colors.LAST
   LOOP
      dbms_output.put_line('Rose color = ' || my_colors(i));
   END LOOP;

-- Look up a name and query the entire row.
   SELECT * INTO my_flower FROM flowers WHERE name = 'Iris';
-- Now COLORS is a field in a record, so we access it with dot notation.
   FOR i IN my_flower.colors.FIRST .. my_flower.colors.LAST
   LOOP
-- Because we have all the table columns in the record, we can refer to NAME also.
      dbms_output.put_line(my_flower.name || ' color = ' || my_flower.colors(i));
   END LOOP;

-- We can replace a set of colors by making a new collection and using it
-- in an UPDATE statement.
   new_colors := ColorList('Red','Yellow','White','Pink');
   UPDATE flowers SET colors = new_colors WHERE name = 'Rose';

-- Or we can modify the original collection and use it in the UPDATE.
-- We'll add a new final element and fill in a value.
   my_flower.colors.EXTEND(1);
   my_flower.colors(my_flower.colors.COUNT) := 'Yellow';
   UPDATE flowers SET colors = my_flower.colors WHERE name = my_flower.name;

-- We can even treat the nested table column like a real table and
-- insert, update, or delete elements.
-- The TABLE operator makes the statement apply to the nested table produced by the subquery.

   INSERT INTO TABLE(SELECT colors FROM flowers WHERE name = 'Rose') VALUES('Black');
   DELETE FROM TABLE(SELECT colors FROM flowers WHERE name = 'Rose') WHERE column_value = 'Yellow';
   UPDATE TABLE(SELECT colors FROM flowers WHERE name = 'Iris')
      SET column_value = 'Indigo' WHERE column_value = 'Purple';

   COMMIT;
END;
/

DROP TABLE flowers;
DROP TYPE ColorList;

Within PL/SQL, you can manipulate the nested table by looping through its elements, using methods such as TRIM or EXTEND, and updating some or all of the elements. Afterwards, you can store the updated table in the database again.

Example 5-28 Updating a Nested Table within a Database Table
You can revise the list of courses offered by the English Department:

DECLARE
   new_courses CourseList :=
      CourseList('Expository Writing',
                 'Film and Literature',
                 'Discursive Writing',
                 'Modern English Grammar',
                 'Realism and Naturalism',
                 'Introduction to Shakespeare',
                 'Modern Drama',
                 'The Short Story',
                 'The American Novel',
                 '20th-Century Poetry',
                 'Advanced Workshop in Poetry');
BEGIN
   UPDATE department
      SET courses = new_courses WHERE name = 'English';
END;

Using PL/SQL Varrays with INSERT, UPDATE, and SELECT Statements

This example shows how you can transfer varrays between PL/SQL variables and SQL tables. You can insert table rows containing varrays, update a row to replace its varray, and select varrays into PL/SQL variables. You cannot update or delete individual varray elements directly with SQL; you have to select the varray from the table, change it in PL/SQL, then update the table to include the new varray.

-- By using a varray, we put an upper limit on the number of elements
-- and ensure they always come back in the same order.
CREATE TYPE RainbowTyp AS VARRAY(7) OF VARCHAR2(64);
/

CREATE TABLE rainbows (language VARCHAR2(64), colors RainbowTyp);

BEGIN
   INSERT INTO rainbows VALUES('English', RainbowTyp('Red','Orange','Yellow','Green','Blue','Indigo','Violet'));
   INSERT INTO rainbows VALUES('Francais', RainbowTyp('Rouge','Orange','Jaune','Vert','Bleu','Indigo','Violet'));
   COMMIT;
END;
/

DECLARE
   new_colors RainbowTyp := RainbowTyp('Crimson','Orange','Amber','Forest','Azure','Indigo','Violet');
   some_colors RainbowTyp;
BEGIN
   UPDATE rainbows SET colors  = new_colors WHERE language = 'English';
   COMMIT;
   SELECT colors INTO some_colors FROM rainbows WHERE language = 'Francais';
   FOR i IN some_colors.FIRST .. some_colors.LAST
   LOOP
      dbms_output.put_line('Color = ' || some_colors(i));
   END LOOP;
END;
/

DROP TABLE rainbows;
DROP TYPE RainbowTyp;

Manipulating Individual Collection Elements with SQL

By default, SQL operations store and retrieve whole collections rather than individual elements. To manipulate the individual elements of a collection with SQL, use the TABLE operator. The TABLE operator uses a subquery to extract the varray or nested table, so that the INSERT, UPDATE, or DELETE statement applies to the nested table rather than the top-level table.

Example 5-29 Performing INSERT, UPDATE, and DELETE Operations on PL/SQL Nested Tables
To perform DML operations on a PL/SQL nested table, use the operators TABLE and CAST. This way, you can do set operations on nested tables using SQL notation, without actually storing the nested tables in the database.
The operands of CAST are PL/SQL collection variable and a SQL collection type (created by the CREATE TYPE statement). CAST converts the PL/SQL collection to the SQL type.

DECLARE
   revised CourseList :=
      CourseList(Course(1002, 'Expository Writing', 3),
                 Course(2020, 'Film and Literature', 4),
                 Course(4210, '20th-Century Poetry', 4),
                 Course(4725, 'Advanced Workshop in Poetry', 5));
   num_changed INTEGER;
BEGIN
   SELECT COUNT(*) INTO num_changed
      FROM TABLE(CAST(revised AS CourseList)) new,
      TABLE(SELECT courses FROM department
         WHERE name = 'English') AS old
      WHERE new.course_no = old.course_no AND
         (new.title != old.title OR new.credits != old.credits);
   dbms_output.put_line(num_changed);
END;

Using Multilevel Collections

In addition to collections of scalar or object types, you can also create collections whose elements are collections. For example, you can create a nested table of varrays, a varray of varrays, a varray of nested tables, and so on.
When creating a nested table of nested tables as a column in SQL, check the syntax of the CREATE TABLE statement to see how to define the storage table.
Here are some examples showing the syntax and possibilities for multilevel collections.

Example 5-30 Multilevel VARRAY

declare
 type t1 is varray(10) of integer;
 type nt1 is varray(10) of t1; -- multilevel varray type
 va t1 := t1(2,3,5);
-- initialize multilevel varray
 nva nt1 := nt1(va, t1(55,6,73), t1(2,4), va);
 i integer;
 va1 t1;
begin
 -- multilevel access
 i := nva(2)(3); -- i will get value 73
 dbms_output.put_line('I = ' || i);
 -- add a new varray element to nva
 nva.extend;

-- replace inner varray elements
 nva(5) := t1(56, 32);
 nva(4) := t1(45,43,67,43345);
-- replace an inner integer element
 nva(4)(4) := 1; -- replaces 43345 with 1
-- add a new element to the 4th varray element
-- and store integer 89 into it.
 nva(4).extend;
 nva(4)(5) := 89;
end;
/

Example 5-31 Multilevel Nested Table

declare
 type tb1 is table of varchar2(20);
 type ntb1 is table of tb1; -- table of table elements
 type tv1 is varray(10) of integer;
 type ntb2 is table of tv1; -- table of varray elements

 vtb1 tb1 := tb1('one', 'three');
 vntb1 ntb1 := ntb1(vtb1);
 vntb2 ntb2 := ntb2(tv1(3,5), tv1(5,7,3));  -- table of varray elements
begin
 vntb1.extend;
 vntb1(2) := vntb1(1);
-- delete the first element in vntb1
 vntb1.delete(1);
-- delete the first string from the second table in the nested table
 vntb1(2).delete(1);
end;
/

Example 5-32 Multilevel Associative Array

declare
 type tb1 is table of integer index by binary_integer;
-- the following is index-by table of index-by tables
 type ntb1 is table of tb1 index by binary_integer;
 type va1 is varray(10) of varchar2(20);
-- the following is index-by table of varray elements
 type ntb2 is table of va1 index by binary_integer;

 v1 va1 := va1('hello', 'world');
 v2 ntb1;
 v3 ntb2;
 v4 tb1;
 v5 tb1; -- empty table
begin
 v4(1) := 34;
 v4(2) := 46456;
 v4(456) := 343;
 v2(23) := v4;
 v3(34) := va1(33, 456, 656, 343);
-- assign an empty table to v2(35) and try again
   v2(35) := v5;
   v2(35)(2) := 78; -- it works now
end;
/

Example 5-33 Multilevel Collections and Bulk SQL

create type t1 is varray(10) of integer;
/
create table tab1 (c1 t1);

insert into tab1 values (t1(2,3,5));
insert into tab1 values (t1(9345, 5634, 432453));

declare
 type t2 is table of t1;
 v2 t2;
begin
 select c1  BULK COLLECT INTO v2 from tab1;
 dbms_output.put_line(v2.count); -- prints 2
end;
/

drop table tab1;
drop type t1;

Using Collection Methods

These collection methods make collections easier to use, and make your applications easier to maintain:

EXISTS

COUNT

LIMIT

FIRST and LAST

PRIOR and NEXT

EXTEND

TRIM

DELETE

A collection method is a built-in function or procedure that operates on collections and is called using dot notation.
Collection methods cannot be called from SQL statements.
EXTEND and TRIM cannot be used with associative arrays.
EXISTS, COUNT, LIMIT, FIRST, LAST, PRIOR, and NEXT are functions; EXTEND, TRIM, and DELETE are procedures.
EXISTS, PRIOR, NEXT, TRIM, EXTEND, and DELETE take parameters corresponding to collection subscripts, which are usually integers but can also be strings for associative arrays.
Only EXISTS can be applied to atomically null collections. If you apply another method to such collections, PL/SQL raises COLLECTION_IS_NULL.

Checking If a Collection Element Exists (EXISTS Method)

EXISTS(n) returns TRUE if the nth element in a collection exists. Otherwise, EXISTS(n) returns FALSE. By combining EXISTS with DELETE, you can work with sparse nested tables. You can also use EXISTS to avoid referencing a nonexistent element, which raises an exception. When passed an out-of-range subscript, EXISTS returns FALSE instead of raising SUBSCRIPT_OUTSIDE_LIMIT.

DECLARE
   TYPE NumList IS TABLE OF INTEGER;
   n NumList := NumList(1,3,5,7);
BEGIN
   n.DELETE(2); -- Delete the second element
   IF n.EXISTS(1) THEN
      dbms_output.put_line('OK, element #1 exists.');
   END IF;
   IF n.EXISTS(2) = FALSE THEN
      dbms_output.put_line('OK, element #2 has been deleted.');
   END IF;
   IF n.EXISTS(99) = FALSE THEN
      dbms_output.put_line('OK, element #99 does not exist at all.');
   END IF;
END;
/

Counting the Elements in a Collection (COUNT Method)

COUNT returns the number of elements that a collection currently contains:

DECLARE
   TYPE NumList IS TABLE OF NUMBER;
   n NumList := NumList(2,4,6,8); -- Collection starts with 4 elements.
BEGIN
   dbms_output.put_line('There are ' || n.COUNT || ' elements in N.');
   n.EXTEND(3); -- Add 3 new elements at the end.
   dbms_output.put_line('Now there are ' || n.COUNT || ' elements in N.');
   n := NumList(86,99); -- Assign a completely new value with 2 elements.
   dbms_output.put_line('Now there are ' || n.COUNT || ' elements in N.');
   n.TRIM(2); -- Remove the last 2 elements, leaving none.
   dbms_output.put_line('Now there are ' || n.COUNT || ' elements in N.');
END;
/

COUNT is useful because the current size of a collection is not always known. For example, you can fetch a column of Oracle data into a nested table, where the number of elements depends on the size of the result set.
For varrays, COUNT always equals LAST. You can increase or decrease the size of a varray using the EXTEND and TRIM methods, so the value of COUNT can change, up to the value of the LIMIT method.
For nested tables, COUNT normally equals LAST. But, if you delete elements from the middle of a nested table, COUNT becomes smaller than LAST. When tallying elements, COUNT ignores deleted elements.

Checking the Maximum Size of a Collection (LIMIT Method)

For nested tables and associative arrays, which have no maximum size, LIMIT returns NULL. For varrays, LIMIT returns the maximum number of elements that a varray can contain/ You specify this limit in the type definition, and can change it later with the TRIM and EXTEND methods. For instance, if the maximum size of varray PROJECTS is 25 elements, the following IF condition is true:

DECLARE
   TYPE Colors IS VARRAY(7) OF VARCHAR2(64);
   c Colors := Colors('Gold','Silver');
BEGIN
   dbms_output.put_line('C has ' || c.COUNT || ' elements now.');
   dbms_output.put_line('C''s type can hold a maximum of ' || c.LIMIT || ' elements.');
   dbms_output.put_line('The maximum number you can use with C.EXTEND() is ' || (c.LIMIT - c.COUNT));
END;
/

Finding the First or Last Collection Element (FIRST and LAST Methods)

FIRST and LAST return the first and last (smallest and largest) index numbers in a collection that uses integer subscripts.
For an associative array with VARCHAR2 key values, the lowest and highest key values are returned. By default, the order is based on the binary values of the characters in the string. If the NLS_COMP initialization parameter is set to ANSI, the order is based on the locale-specific sort order specified by the NLS_SORT initialization parameter.
If the collection is empty, FIRST and LAST return NULL.
If the collection contains only one element, FIRST and LAST return the same index value.
The following example shows how to use FIRST and LAST to iterate through the elements in a collection that has consecutive subscripts:

DECLARE
   TYPE NumList IS TABLE OF NUMBER;
   n NumList := NumList(1,3,5,7);
   counter INTEGER;
BEGIN
   dbms_output.put_line('N''s first subscript is ' || n.FIRST);
   dbms_output.put_line('N''s last subscript is ' || n.LAST);

-- When the subscripts are consecutive starting at 1, it's simple to loop through them.
   FOR i IN n.FIRST .. n.LAST
   LOOP
      dbms_output.put_line('Element #' || i || ' = ' || n(i));
   END LOOP;

   n.DELETE(2); -- Delete second element.
-- When the subscripts have gaps or the collection might be uninitialized,
-- the loop logic is more extensive. We start at the first element, and
-- keep looking for the next element until there are no more.
   IF n IS NOT NULL THEN
      counter := n.FIRST;
      WHILE counter IS NOT NULL
      LOOP
         dbms_output.put_line('Element #' || counter || ' = ' || n(counter));
         counter := n.NEXT(counter);
      END LOOP;
   ELSE
      dbms_output.put_line('N is null, nothing to do.');
   END IF;
END;
/

For varrays, FIRST always returns 1 and LAST always equals COUNT.
For nested tables, normally FIRST returns 1 and LAST equals COUNT. But if you delete elements from the beginning of a nested table, FIRST returns a number larger than 1. If you delete elements from the middle of a nested table, LAST becomes larger than COUNT.
When scanning elements, FIRST and LAST ignore deleted elements.

Looping Through Collection Elements (PRIOR and NEXT Methods)

PRIOR(n) returns the index number that precedes index n in a collection. NEXT(n) returns the index number that succeeds index n. If n has no predecessor, PRIOR(n) returns NULL. If n has no successor, NEXT(n) returns NULL.
For associative arrays with VARCHAR2 keys, these methods return the appropriate key value; ordering is based on the binary values of the characters in the string, unless the NLS_COMP initialization parameter is set to ANSI, in which case the ordering is based on the locale-specific sort order specified by the NLS_SORT initialization parameter.
These methods are more reliable than looping through a fixed set of subscript values, because elements might be inserted or deleted from the collection during the loop. This is especially true for associative arrays, where the subscripts might not be in consecutive order and so the sequence of subscripts might be (1,2,4,8,16) or ('A','E','I','O','U').

DECLARE
   TYPE NumList IS TABLE OF NUMBER;
   n NumList := NumList(1966,1971,1984,1989,1999);
BEGIN
   dbms_output.put_line('The element after #2 is #' || n.NEXT(2));
   dbms_output.put_line('The element before #2 is #' || n.PRIOR(2));
   n.DELETE(3); -- Delete an element to show how NEXT can handle gaps.
   dbms_output.put_line('Now the element after #2 is #' || n.NEXT(2));
   IF n.PRIOR(n.FIRST) IS NULL THEN
      dbms_output.put_line('Can''t get PRIOR of the first element or NEXT of the last.');
   END IF;
END;
/

You can use PRIOR or NEXT to traverse collections indexed by any series of subscripts. The following example uses NEXT to traverse a nested table from which some elements have been deleted:

DECLARE
   TYPE NumList IS TABLE OF NUMBER;
   n NumList := NumList(1,3,5,7);
   counter INTEGER;
BEGIN
   n.DELETE(2); -- Delete second element.
-- When the subscripts have gaps, the loop logic is more extensive. We start at the
-- first element, and keep looking for the next element until there are no more.
   counter := n.FIRST;
   WHILE counter IS NOT NULL
   LOOP
      dbms_output.put_line('Counting up: Element #' || counter || ' = ' || n(counter));
      counter := n.NEXT(counter);
   END LOOP;

-- Run the same loop in reverse order.
   counter := n.LAST;
   WHILE counter IS NOT NULL
   LOOP
      dbms_output.put_line('Counting down: Element #' || counter || ' = ' || n(counter));
      counter := n.PRIOR(counter);
   END LOOP;
END;
/

When traversing elements, PRIOR and NEXT skip over deleted elements.

Increasing the Size of a Collection (EXTEND Method)

To increase the size of a nested table or varray, use EXTEND.
You cannot use EXTEND with index-by tables.
This procedure has three forms:

• EXTEND appends one null element to a collection.
• EXTEND(n) appends n null elements to a collection.
• EXTEND(n,i) appends n copies of the ith element to a collection.

You cannot use EXTEND to add elements to an uninitialized.
If you impose the NOT NULL constraint on a TABLE or VARRAY type, you cannot apply the first two forms of EXTEND to collections of that type.
EXTEND operates on the internal size of a collection, which includes any deleted elements. If EXTEND encounters deleted elements, it includes them in its tally. PL/SQL keeps placeholders for deleted elements so that you can re-create them by assigning new values.

DECLARE
   TYPE NumList IS TABLE OF INTEGER;
   n NumList := NumList(2,4,6,8);
   x NumList := NumList(1,3);
   PROCEDURE print_numlist(the_list NumList) IS
      output VARCHAR2(128);
   BEGIN
      FOR i IN the_list.FIRST .. the_list.LAST
      LOOP
         output := output || NVL(TO_CHAR(the_list(i)),'NULL') || ' ';
      END LOOP;
      dbms_output.put_line(output);
   END;
BEGIN
   dbms_output.put_line('At first, N has ' || n.COUNT || ' elements.');
   n.EXTEND(5); -- Add 5 elements at the end.
   dbms_output.put_line('Now N has ' || n.COUNT || ' elements.');
-- Elements 5, 6, 7, 8, and 9 are all NULL.
   print_numlist(n);

   dbms_output.put_line('At first, X has ' || x.COUNT || ' elements.');
   x.EXTEND(4,2); -- Add 4 elements at the end.
   dbms_output.put_line('Now X has ' || x.COUNT || ' elements.');
-- Elements 3, 4, 5, and 6 are copies of element #2.
   print_numlist(x);
END;
/

When it includes deleted elements, the internal size of a nested table differs from the values returned by COUNT and LAST. For instance, if you initialize a nested table with five elements, then delete elements 2 and 5, the internal size is 5, COUNT returns 3, and LAST returns 4. All deleted elements, regardless of position, are treated alike.

Decreasing the Size of a Collection (TRIM Method)

This procedure has two forms:

• TRIM removes one element from the end of a collection.
• TRIM(n) removes n elements from the end of a collection.

For example, this statement removes the last three elements from nested table courses:

DECLARE
   TYPE NumList IS TABLE OF NUMBER;
   n NumList := NumList(1,2,3,5,7,11);
   PROCEDURE print_numlist(the_list NumList) IS
      output VARCHAR2(128);
   BEGIN
      IF n.COUNT = 0 THEN
         dbms_output.put_line('No elements in collection.');
      ELSE
         FOR i IN the_list.FIRST .. the_list.LAST
         LOOP
            output := output || NVL(TO_CHAR(the_list(i)),'NULL') || ' ';
         END LOOP;
         dbms_output.put_line(output);
      END IF;
   END;
BEGIN
   print_numlist(n);
   n.TRIM(2); -- Remove last 2 elements.
   print_numlist(n);
   n.TRIM; -- Remove last element.
   print_numlist(n);
   n.TRIM(n.COUNT); -- Remove all remaining elements.
   print_numlist(n);

-- If too many elements are specified, TRIM raises the exception SUBSCRIPT_BEYOND_COUNT.
   BEGIN
      n := NumList(1,2,3);
      n.TRIM(100);
      EXCEPTION
         WHEN SUBSCRIPT_BEYOND_COUNT THEN
            dbms_output.put_line('I guess there weren''t 100 elements that could be trimmed.');
   END;

-- When elements are removed by DELETE, placeholders are left behind. TRIM counts these
-- placeholders as it removes elements from the end.

   n := NumList(1,2,3,4);
   n.DELETE(3);  -- delete element 3
-- At this point, n contains elements (1,2,4).
-- TRIMming the last 2 elements removes the 4 and the placeholder, not 4 and 2.
   n.TRIM(2);
   print_numlist(n);
END;
/
END;
/

If n is too large, TRIM(n) raises SUBSCRIPT_BEYOND_COUNT.
TRIM operates on the internal size of a collection. If TRIM encounters deleted elements, it includes them in its tally. Consider the following example:

DECLARE
   TYPE CourseList IS TABLE OF VARCHAR2(10); 
   courses CourseList;
BEGIN
   courses := CourseList('Biol 4412', 'Psyc 3112', 'Anth 3001');
   courses.DELETE(courses.LAST);  -- delete element 3
   /* At this point, COUNT equals 2, the number of valid
      elements remaining. So, you might expect the next 
      statement to empty the nested table by trimming 
      elements 1 and 2. Instead, it trims valid element 2 
      and deleted element 3 because TRIM includes deleted 
      elements in its tally. */
   courses.TRIM(courses.COUNT);
   dbms_output.put_line(courses(1));  -- prints 'Biol 4412'
END;
/

In general, do not depend on the interaction between TRIM and DELETE. It is better to treat nested tables like fixed-size arrays and use only DELETE, or to treat them like stacks and use only TRIM and EXTEND.
Because PL/SQL does not keep placeholders for trimmed elements, you cannot replace a trimmed element simply by assigning it a new value.

Deleting Collection Elements (DELETE Method)

This procedure has various forms:

• DELETE removes all elements from a collection.
• DELETE(n) removes the nth element from an associative array with a numeric key or a nested table. If the associative array has a string key, the element corresponding to the key value is deleted. If n is null, DELETE(n) does nothing.
• DELETE(m,n) removes all elements in the range m..n from an associative array or nested table. If m is larger than n or if m or n is null, DELETE(m,n) does nothing.

For example:

DECLARE
   TYPE NumList IS TABLE OF NUMBER;
   n NumList := NumList(10,20,30,40,50,60,70,80,90,100);
   TYPE NickList IS TABLE OF VARCHAR2(64) INDEX BY VARCHAR2(32);
   nicknames NickList;
BEGIN
   n.DELETE(2);    -- deletes element 2 
   n.DELETE(3,6);  -- deletes elements 3 through 6 
   n.DELETE(7,7);  -- deletes element 7 
   n.DELETE(6,3);  -- does nothing since 6 > 3

   n.DELETE;      -- deletes all elements

   nicknames('Bob') := 'Robert';
   nicknames('Buffy') := 'Esmerelda';
   nicknames('Chip') := 'Charles';
   nicknames('Dan') := 'Daniel';
   nicknames('Fluffy') := 'Ernestina';
   nicknames('Rob') := 'Robert';

   nicknames.DELETE('Chip'); -- deletes element denoted by this key
   nicknames.DELETE('Buffy','Fluffy'); -- deletes elements with keys in this alphabetic range
END;
/

Varrays always have consecutive subscripts, so you cannot delete individual elements except from the end (by using the TRIM method).
If an element to be deleted does not exist, DELETE simply skips it; no exception is raised. PL/SQL keeps placeholders for deleted elements, so you can replace a deleted element by assigning it a new value.
DELETE lets you maintain sparse nested tables. You can store sparse nested tables in the database, just like any other nested tables.
The amount of memory allocated to a nested table can increase or decrease dynamically. As you delete elements, memory is freed page by page. If you delete the entire table, all the memory is freed.

Applying Methods to Collection Parameters

Within a subprogram, a collection parameter assumes the properties of the argument bound to it. You can apply the built-in collection methods (FIRST, LAST, COUNT, and so on) to such parameters. You can create general-purpose subprograms that take collection parameters and iterate through their elements, add or delete elements, and so on.
Note: For varray parameters, the value of LIMIT is always derived from the parameter type definition, regardless of the parameter mode.

Avoiding Collection Exceptions

In most cases, if you reference a nonexistent collection element, PL/SQL raises a predefined exception. Consider the following example:

DECLARE
   TYPE NumList IS TABLE OF NUMBER;
   nums NumList;  -- atomically null
BEGIN
   /* Assume execution continues despite the raised exceptions. */
   nums(1) := 1;                      -- raises COLLECTION_IS_NULL       (1)
   nums := NumList(1,2);              -- initialize nested table
   nums(NULL) := 3;                   -- raises VALUE_ERROR              (2)
   nums(0) := 3;                      -- raises SUBSCRIPT_OUTSIDE_LIMIT  (3)
   nums(3) := 3;                      -- raises SUBSCRIPT_BEYOND_COUNT   (4)
   nums.DELETE(1);                    -- delete element 1
   IF nums(1) = 1 THEN NULL; END IF;  -- raises NO_DATA_FOUND            (5)
END;
/

In the first case, the nested table is atomically null. In the second case, the subscript is null. In the third case, the subscript is outside the allowed range. In the fourth case, the subscript exceeds the number of elements in the table. In the fifth case, the subscript designates a deleted element.
The following list shows when a given exception is raised:

Collection Exception	Raised when...
COLLECTION_IS_NULL	you try to operate on an atomically null collection.
NO_DATA_FOUND	a subscript designates an element that was deleted, or a nonexistent element of an associative array.
SUBSCRIPT_BEYOND_COUNT	a subscript exceeds the number of elements in a collection.
SUBSCRIPT_OUTSIDE_LIMIT	a subscript is outside the allowed range.
VALUE_ERROR	a subscript is null or not convertible to the key type. This exception might occur if the key is defined as a PLS_INTEGER range, and the subscript is outside this range.

In some cases, you can pass invalid subscripts to a method without raising an exception. For instance, when you pass a null subscript to procedure DELETE, it does nothing. You can replace deleted elements by assigning values to them, without raising NO_DATA_FOUND:

DECLARE
   TYPE NumList IS TABLE OF NUMBER;
   nums NumList := NumList(10,20,30);  -- initialize table
BEGIN
   nums.DELETE(-1);  -- does not raise SUBSCRIPT_OUTSIDE_LIMIT
   nums.DELETE(3);   -- delete 3rd element
   dbms_output.put_line(nums.COUNT);  -- prints 2
   nums(3) := 30;    -- allowed; does not raise NO_DATA_FOUND
   dbms_output.put_line(nums.COUNT);  -- prints 3
END;
/

Packaged collection types and local collection types are never compatible. For example, suppose you want to call the following packaged procedure:

CREATE PACKAGE pkg AS
   TYPE NumList IS TABLE OF NUMBER;
   PROCEDURE print_numlist (nums NumList);
END pkg;
/

DECLARE
   TYPE NumList IS TABLE OF NUMBER;
   n1  pkg.NumList := pkg.NumList(2,4); -- Type from the package.
   n2 NumList := NumList(6,8);          -- Local type.
BEGIN
   pkg.print_numlist(n1);
-- The packaged procedure can't accept a value of the local type.
   pkg.print_numlist(n2);  -- Causes a compilation error.
END;
/

DROP PACKAGE pkg;

The second procedure call fails, because the packaged and local VARRAY types are incompatible despite their identical definitions.

What Is a PL/SQL Record?

A record is a group of related data items stored in fields, each with its own name and datatype. You can think of a record as a variable that can hold a table row, or some columns from a table row. The fields correspond to table columns.
The %ROWTYPE attribute lets you declare a record that represents a row in a database table, without listing all the columns. Your code keeps working even after columns are added to the table. If you want to represent a subset of columns in a table, or columns from different tables, you can define a view or declare a cursor to select the right columns and do any necessary joins, and then apply %ROWTYPE to the view or cursor.

Defining and Declaring Records

To create records, you define a RECORD type, then declare records of that type. You can also create or find a table, view, or PL/SQL cursor with the values you want, and use the %ROWTYPE attribute to create a matching record.
You can define RECORD types in the declarative part of any PL/SQL block, subprogram, or package. When you define your own RECORD type, you can specify a NOT NULL constraint on fields, or give them default values.

DECLARE
-- Declare a record type with 3 fields.
  TYPE rec1_t IS RECORD (field1 VARCHAR2(16), field2 NUMBER, field3 DATE);
-- For any fields declared NOT NULL, we must supply a default value.
  TYPE rec2_t IS RECORD (id INTEGER NOT NULL := -1, name VARCHAR2(64) NOT NULL := '[anonymous]');

-- Declare record variables of the types declared above.
  rec1 rec1_t;
  rec2 rec2_t;

-- Declare a record variable that can hold a row from the EMPLOYEES table.
-- The fields of the record automatically match the names and types of the columns.
-- Don't need a TYPE declaration in this case.
  rec3 employees%ROWTYPE;

-- Or we can mix fields that are table columns with user-defined fields.
  TYPE rec4_t IS RECORD (first_name employees.first_name%TYPE, last_name employees.last_name%TYPE, rating NUMBER);
  rec4 rec4_t;

BEGIN
-- Read and write fields using dot notation
  rec1.field1 := 'Yesterday';
  rec1.field2 := 65;
  rec1.field3 := TRUNC(SYSDATE-1);

-- We didn't fill in the NAME field, so it takes the default value declared above.
  dbms_output.put_line(rec2.name);
END;
/

To store a record in the database, you can specify it in an INSERT or UPDATE statement, if its fields match the columns in the table:

...

You can use %TYPE to specify a field type corresponding to a table column type. Your code keeps working even if the column type is changed (for example, to increase the length of a VARCHAR2 or the precision of a NUMBER). The following example defines RECORD types to hold information about a department:

DECLARE
-- Best: use %ROWTYPE instead of specifying each column.
-- Using <cursor>%ROWTYPE instead of <table>%ROWTYPE since we only want some columns.
-- Declaring the cursor doesn't run the query, so no performance hit.
   CURSOR c1 IS SELECT department_id, department_name, location_id FROM departments;
   rec1 c1%ROWTYPE;

-- Use <column>%TYPE in field declarations to avoid problems if the column types change.
   TYPE DeptRec2 IS RECORD (dept_id   departments.department_id%TYPE, dept_name departments.department_name%TYPE, dept_loc departments.location_id%TYPE);
   rec2 DeptRec2;

-- Final technique, writing out each field name and specifying the type directly, is
-- clumsy and unmaintainable for working with table data. Use only for all-PL/SQL code.
   TYPE DeptRec3 IS RECORD (dept_id NUMBER, dept_name VARCHAR2(14), dept_loc VARCHAR2(13));
   rec3 DeptRec3;
BEGIN
   NULL;
END;
/

PL/SQL lets you define records that contain objects, collections, and other records (called nested records). However, records cannot be attributes of object types.

Using Records as Procedure Parameters and Function Return Values

Records are easy to process using stored procedures because you can pass just one parameter, instead of a separate parameter for each field. For example, you might fetch a table row from the EMPLOYEES table into a record, then pass that row as a parameter to a function that computed that employee's vacation allowance or some other abstract value. The function could access all the information about that employee by referring to the fields in the record.
The next example shows how to return a record from a function. To make the record type visible across multiple stored functions and stored procedures, declare the record type in a package specification.

DECLARE
   TYPE EmpRec IS RECORD (
      emp_id    NUMBER(4)
      last_name VARCHAR2(10),
      dept_num  NUMBER(2),
      job_title VARCHAR2(9), 
      salary    NUMBER(7,2));
   FUNCTION nth_highest_salary (n INTEGER) RETURN EmpRec IS ...
BEGIN
   NULL;
END;
/

Like scalar variables, user-defined records can be declared as the formal parameters of procedures and functions:

DECLARE
   TYPE EmpRec IS RECORD ( 
      emp_id    emp.empno%TYPE,
      last_name VARCHAR2(10),
      job_title VARCHAR2(9),
      salary    NUMBER(7,2));
   ...
   PROCEDURE raise_salary (emp_info EmpRec);
BEGIN
   ...
END;
/

Assigning Values to Records

To set all the fields in a record to default values, assign to it an uninitialized record of the same type:

DECLARE
   TYPE RecordTyp IS RECORD (field1 NUMBER, field2 VARCHAR2(32) DEFAULT 'something');
   rec1 RecordTyp;
   rec2 RecordTyp;
BEGIN
-- At first, rec1 has the values we assign.
   rec1.field1 := 100; rec1.field2 := 'something else';
-- Assigning an empty record to rec1 resets fields to their default values.
-- Field1 is NULL and field2 is 'something' (because of the DEFAULT clause above).
   rec1 := rec2;
   dbms_output.put_line('Field1 = ' || NVL(TO_CHAR(rec1.field1),'<NULL>') || ', field2 = ' || rec1.field2);
END;
/

You can assign a value to a field in a record using an assignment statement with dot notation:

emp_info.last_name := 'Fields';

Instead of assigning values separately to each field in a record, you can assign values to all fields at once.
You can assign one user-defined record to another if they have the same datatype. Having fields that match exactly is not enough. Consider the following example:

DECLARE
-- Two identical type declarations.
   TYPE DeptRec1 IS RECORD ( dept_num  NUMBER(2), dept_name VARCHAR2(14));
   TYPE DeptRec2 IS RECORD ( dept_num  NUMBER(2), dept_name VARCHAR2(14));
   dept1_info DeptRec1;
   dept2_info DeptRec2;
   dept3_info DeptRec2;
BEGIN
-- Not allowed; different datatypes, even though fields are the same.
--      dept1_info := dept2_info; 
-- This assignment is OK because the records have the same type.
   dept2_info := dept3_info;
END;
/

You can assign a %ROWTYPE record to a user-defined record if their fields match in number and order, and corresponding fields have the same datatypes:

DECLARE
   TYPE RecordTyp IS RECORD (last employees.last_name%TYPE, id employees.employee_id%TYPE);
   CURSOR c1 IS SELECT last_name, employee_id FROM employees;

-- Rec1 and rec2 have different types. But because rec2 is based on a %ROWTYPE, we can
-- assign is to rec1 as long as they have the right number of fields and the fields
-- have the right datatypes.
   rec1 RecordTyp;
   rec2 c1%ROWTYPE;
BEGIN
   SELECT last_name, employee_id INTO rec2 FROM employees WHERE ROWNUM < 2;
   rec1 := rec2;
   dbms_output.put_line('Employee #' || rec1.id || ' = ' || rec1.last);
END;
/

You can also use the SELECT or FETCH statement to fetch column values into a record. The columns in the select-list must appear in the same order as the fields in your record.

DECLARE
   TYPE RecordTyp IS RECORD (last employees.last_name%TYPE, id employees.employee_id%TYPE);
   rec1 RecordTyp;
BEGIN
   SELECT last_name, employee_id INTO rec1 FROM employees WHERE ROWNUM < 2;
   dbms_output.put_line('Employee #' || rec1.id || ' = ' || rec1.last);
END;
/

You cannot assign a list of values to a record using an assignment statement. There is no constructor-like notation for records.

Comparing Records

Records cannot be tested for nullity, or compared for equality, or inequality.
If you want to make such comparisons, write your own function that accepts two records as parameters and does the appropriate checks or comparisons on the corresponding fields.

Inserting PL/SQL Records into the Database

A PL/SQL-only extension of the INSERT statement lets you insert records into database rows, using a single variable of type RECORD or %ROWTYPE in the VALUES clause instead of a list of fields. That makes your code more readable and maintainable.
If you issue the INSERT through the FORALL statement, you can insert values from an entire collection of records.
The number of fields in the record must equal the number of columns listed in the INTO clause, and corresponding fields and columns must have compatible datatypes. To make sure the record is compatible with the table, you might find it most convenient to declare the variable as the type table_name%ROWTYPE.

Example 5-34 Inserting a PL/SQL Record Using %ROWTYPE
This example declares a record variable using a %ROWTYPE qualifier. You can insert this variable without specifying a column list. The %ROWTYPE declaration ensures that the record attributes have exactly the same names and types as the table columns.

DECLARE
   dept_info dept%ROWTYPE;
BEGIN
-- deptno, dname, and loc are the table columns.
-- The record picks up these names from the %ROWTYPE.
  dept_info.deptno := 70;
  dept_info.dname := 'PERSONNEL';
  dept_info.loc := 'DALLAS';
-- Using the %ROWTYPE means we can leave out the column list
-- (deptno, dname, loc) from the INSERT statement.
   INSERT INTO dept VALUES dept_info;
END;
/

Updating the Database with PL/SQL Record Values

A PL/SQL-only extension of the UPDATE statement lets you update database rows using a single variable of type RECORD or %ROWTYPE on the right side of the SET clause, instead of a list of fields.
If you issue the UPDATE through the FORALL statement, you can update a set of rows using values from an entire collection of records.
Also with an UPDATE statement, you can specify a record in the RETURNING clause to retrieve new values into a record. If you issue the UPDATE through the FORALL statement, you can retrieve new values from a set of updated rows into a collection of records.
The number of fields in the record must equal the number of columns listed in the SET clause, and corresponding fields and columns must have compatible datatypes.

Example 5-35 Updating a Row Using a Record
You can use the keyword ROW to represent an entire row:

DECLARE
   dept_info dept%ROWTYPE;
BEGIN
   dept_info.deptno := 30;
   dept_info.dname := 'MARKETING';
   dept_info.loc := 'ATLANTA';
-- The row will have values for the filled-in columns, and null
-- for any other columns.
   UPDATE dept SET ROW = dept_info WHERE deptno = 30;
END;
/

The keyword ROW is allowed only on the left side of a SET clause.
The argument to SET ROW must be a real PL/SQL record, not a subquery that returns a single row.
The record can also contain collections or objects.

Example 5-36 Using the RETURNING Clause with a Record
The INSERT, UPDATE, and DELETE statements can include a RETURNING clause, which returns column values from the affected row into a PL/SQL record variable. This eliminates the need to SELECT the row after an insert or update, or before a delete.
By default, you can use this clause only when operating on exactly one row. When you use bulk SQL, you can use the form RETURNING BULK COLLECT INTO to store the results in one or more collections.
The following example updates the salary of an employee and retrieves the employee's name, job title, and new salary into a record variable:

DECLARE
   TYPE EmpRec IS RECORD (last_name employees.last_name%TYPE, salary employees.salary%TYPE);
   emp_info EmpRec;
   emp_id NUMBER := 100;
BEGIN
   UPDATE employees SET salary = salary * 1.1 WHERE employee_id = emp_id
      RETURNING last_name, salary INTO emp_info;
   dbms_output.put_line('Just gave a raise to ' || emp_info.last_name ||
      ', who now makes ' || emp_info.salary);
   ROLLBACK;
END;
/

Restrictions on Record Inserts/Updates

Currently, the following restrictions apply to record inserts/updates:

• Record variables are allowed only in the following places:
  
  • On the right side of the SET clause in an UPDATE statement
  • In the VALUES clause of an INSERT statement
  • In the INTO subclause of a RETURNING clause
  Record variables are not allowed in a SELECT list, WHERE clause, GROUP BY clause, or ORDER BY clause.
• The keyword ROW is allowed only on the left side of a SET clause. Also, you cannot use ROW with a subquery.
• In an UPDATE statement, only one SET clause is allowed if ROW is used.
• If the VALUES clause of an INSERT statement contains a record variable, no other variable or value is allowed in the clause.
• If the INTO subclause of a RETURNING clause contains a record variable, no other variable or value is allowed in the subclause.
• The following are not supported:
  
  • Nested record types
  • Functions that return a record
  • Record inserts/updates using the EXECUTE IMMEDIATE statement.

Querying Data into Collections of Records

You can use the BULK COLLECT clause with a SELECT INTO or FETCH statement to retrieve a set of rows into a collection of records.

DECLARE
   TYPE EmployeeSet IS TABLE OF employees%ROWTYPE;
   underpaid EmployeeSet; -- Holds set of rows from EMPLOYEES table.

   CURSOR c1 IS SELECT first_name, last_name FROM employees;
   TYPE NameSet IS TABLE OF c1%ROWTYPE;
   some_names NameSet; -- Holds set of partial rows from EMPLOYEES table.

BEGIN
-- With one query, we bring all the relevant data into the collection of records.
   SELECT * BULK COLLECT INTO underpaid FROM employees
      WHERE salary < 2500 ORDER BY salary DESC;

-- Now we can process the data by examining the collection, or passing it to
-- a separate procedure, instead of writing a loop to FETCH each row.
   dbms_output.put_line(underpaid.COUNT || ' people make less than 2500.');
   FOR i IN underpaid.FIRST .. underpaid.LAST
   LOOP
      dbms_output.put_line(underpaid(i).last_name || ' makes ' || underpaid(i).salary);
   END LOOP;

-- We can also bring in just some of the table columns.
-- Here we get the first and last names of 10 arbitrary employees.
   SELECT first_name, last_name BULK COLLECT INTO some_names FROM employees
      WHERE ROWNUM < 11;
   FOR i IN some_names.FIRST .. some_names.LAST
   LOOP
      dbms_output.put_line('Employee = ' || some_names(i).first_name || ' ' || some_names(i).last_name);
   END LOOP;
END;
/