SQL FAQS

                                           SQL FAQ’S

1.   What is constraint? What are the different constraints available in oracle?

A constraint is business rule needs to incorporated in our application. 

• Primary key
• Unique key
• Not null
• Check
• Foreign key

2. What is different between primary key and unique key?

Table can have only primary key, but multiple unique keys can be defined on a table.

Unique can accepts null values and primary does not allow null values.

3. What are the constraints will create indexes?

Primary key and unique constraints will create index.

4. What is foreign key?

The column which has foreign key can contain values of primary key, unique key defined in the same table or other table. A foreign can also refer to NULL value.

5. What are the different option can used with FK?
• On delete Cascade: - F K will be deleting before primary key deletes.
• On delete set null: - F K will be set into NULL when primary key deletes.

6. What is composite constraint?

A constraint defined on two or more columns is called as composite key.

Example: - ename is each dept in unique. Such a constraint can be defined as

Constraint <constraint> primary key (ename, deptno)

7.  How can archive multiple primary keys on a table

By defining key like

            Create table dept

            (

Deptno number primary key,

                        Dname varchar2 (10) Unique Not null – this also acts as PK

);                     

Note: - combination of not null and unique acts as PK.                   

8. By default how the constraint names are stored in Data base?

SYS_Cn where n is number like 123456 these constraints are stored in user_constraints table

9. Name the table where we can see the version of Oracle?

The column BANNER in the table v$version tell us the version of oracle.

10. Can specify the different joins.
• Self Join
• Left outer Join
• Right Outer Join
•  

11. What is significance of  (+) in Joins

           Symbol (+) says add null values for the tables columns which does have matching columns in the other tables.

Ex : -    select  a.empno

,a.sal,

b.dept

,b.loc

,dname

from  emp a , emp b

where a.deptno (+) = b.deptno  The above query will returns the deptno 40 information even thought no employee belogs to dept 40.

Empno             sal                    dept                 loc                   dname

162715                        25000              10                    Bangaloare       softwate

162716                        28000              20                    mysore             H/w

162455                        12000              30                    Mangalore        Slaaes

                                                40                    ITPL                Accounts        

If we don’t specify (+) symbol in query the last record won’t be displayed.

Assume emp has deptno like 10,20,30,50

And dept has deptno like 10,20,30,40

Now query should return all the dept which are in emp and dept.

Select ---

From emp , dept

Where emp.deptno (+) = dept.deptno (+)

The above query fails we should not have (+) on either sides.

We can use “Full outer Join” Or use the following technique.( Read in

Select ---

From emp , dept

Where emp.deptno    = dept.deptno (+)

UNION

Select ---

From emp , dept

Where emp.deptno (+) = dept.deptno 

The output looks like

Empno             sal                    dept                 loc                   dname

162715                        25000              10                    Bangaloare       software

162716                        28000              20                    my sore                        H/w

162455                        12000              30                    Mangalore        Slaaes

                                                40                    ITPL                Accounts

12345              45857                                                             

Empno 12345 may belong to some other dept which is not in dept table.

12. What is Co – related sub query?

A sub query which executes for each row in the main query and return the logical true / false. If this sub query returns the true then main query will pass and displays the required records.

13. What is different between co-related sub query and a sub query?

 Ordinary sub query will execute first and only once, it will returns values to main query, these values are treated as logical OR

 Example: -

Select * from dept where deptno in (

                        Select deptno from dept)

Here sub query “Select deptno from dept” will execute first and returns values 10 , 20, 30 so query looks like

Select * from dept where deptno in (10, 20, 30)

And oracle interprets this query like

Select * from dept where deptno = 10 or deptno = 20 or deptno =30;

Using co-related sub query above query can be write as

Select * from dept where exists

(Select ‘x’ from EMP where emp.deptno = dept.deptno) 

14. Write co-related sub query which returns the dept which have at least employees.

 Select * from dept a

 Where exists (select null from emp b where b.deptno = a.deptno);

15. Write co-related sub query which returns the dept which does not have any employees.

Select * from dept a

Where not exists (select null from emp b where b.deptno = a.deptno);

16. When do use co-related sub query?

If we are extracting data from only one table based on logical existence in other table.

17. When do you for Joining?

We used joins to extract data from two tables based on their existing relation, usually one will be Master table and another will be child table.

18.   Write a query to display EMP name and its manager name from the emp table.

Select a.ename , b.ename

From emp a , emp b

Where a.empno = b.mgrno (+)

19. What are pseudo columns in Oracle?

ROWNUM, ROWID, NEXTVAL, CURRVAL, LEVEL are pseudo columns.

20. What is use of ROWNUM?

ROWNUM can be used to limit the records.

Example: - Assume EMP has 14 records; we want to delete only any 10 records,              

                   A query looks like

Delete from EMP where ROWNUM < 11;

21. What is the order of execution of SQL?
• Select clause,
• From clause
• Where clause,
• Group by
• Having
• Order by

22. What is output of following quires?

Select * from EMP where rownum = 10;

No Rows Selected

Select * from EMP where rownum = 1;

One row will be selected

Select * from EMP where rownum < 10;

9 rows will be selected

Select * from EMP where rownum > 10;

No Rows Selected

23. What is rowid?

Pseudo column ROWID, which represents the unique address of each row in a table.

• Data object (segment) identifier
• Data file identifier
• Block identifier
• Row identifier

 Since it is contains physical address it is very easy to access the records using rowid.

24. Can we use rowid in where clause?

It is not good practice to use rowid in where clause of sql query.

It is usually used in select statements in cursor.

For I in( select rowid , dname, loc from dept where deptno =10)

loop

            --

            --

            Update dept

     Set   loc = i.loc

Where rowid = i.rowid;

25. What are the different set operators in Oracle

Union

Union All

Minus

Intersect

26. What are common requirements for using these operators In between the quires?

The numbers of columns and data type should be same in both quires. But names of the columns may be different.

Ex: -                select deptno, dname   from EMP

                        Union

                        Select department, departmentname from dept;

In the above quires have two columns and deptno, department should be same data type and dname, departmentname should be have same data type.

27. How do you enhance IF then Else in Sql.

   Decode Function can be used to incorporate such requirements.

Example: - If deptno 10 then display ‘TEN’ if 20…....So

Select decode (deptno, 10,’TEN’,

20,’TWENTY’,

30,’THIRTY’,

40,’FOURTY’,

’UNKNOW DEPT’)

 FROM dept;

28. Write a query to display number of male and female in a class ?

Table name      :- class

Column name

Name                           varchar2 (10)

Sex                              char (1) 

SELECT COUNT (DECODE (SEX,'M', SEX, NULL)) male,

                           COUNT (DECODE (SEX,'F', SEX, NULL)) female

 FROM class;  

29. What is NVL function?

NVL Function is used to replace the NULL values with specific values of compatible data types,

Example: - select NVL (comm., 0) from EMP;

Above query replaces the NULL with 0 

 Write a query to select all the EMP whose comm is less then 1000.

 Select * from EMP where comm < 1000,

 The above query does not returns the employee’s information even if comm is null, So I above query can be write it these ways

Select * from EMP where comm < 1000 OR comm IS NULL;,

Select * from EMP where NVL (comm, 0) < 1000 

NVL function has its own limitation; NVL function can replaces NULL values into specific values of compatible data types. Assume Id is column of data type number, then following query fails since number is not a compatible data type with string.

Select NVL (EmpId, ‘UN KNOWN id’) from EMP;

30. What the differences are between DECODE and nul functions?

DECODE function is useful to achive if then else in SQL for any given values, where as NVL function is useful only to replace NULL values.

NVL function replaces only compatible data type values, Say Number to Number, Number to char, char to date. But decode can be used irrespective of data type.

31.  write a query to display the names  with right alignments 

 Select RPAD (name, 25,' ') from EMP;

32. What is different between delete and truncate

Delete is a DML statement since it creates the UNDO segment we can rollback.

Truncate is DDL, it won’t generates the undo segment we can’t rollback the Trans.

We can fire triggers for delete statements. But it is not true for truncate command.

33. What are differences between drop and truncate command?

DROP will completely removes the structure form the data base, while truncate removes only the records but leaves the structure unaltered.

34. Write a query to delete the duplicate rows. (Assume EMPNO is duplicated )

Delete from EMP where rowid not in (

Select min (rowid) from EMP group by empno);

35. How to you display alternative rows from a table. ?

Select * from EMP where MOD (ASCII (SUBSTR (rowid,-1)), 2) =0;

36.  Display the deptno which has more then 5 employees

Select deptno from EMP group by deptno having count (deptno) > 5.

37. Display the deptno and maximum salary for each deptno

SELECT deptno, MAX (sal) FROM EMP GROUP BY deptno;           

38. Display all the employees’ names they having maximum salary.

Select ename, sal from EMP where sal in (select max (sal) from emp);

39. select all the employees they joined after 10/jan/1970

“Select * from EMP where hiredate > ’10-JAN-1970’”

The above query does not return any records because where clause fails, by default hiredate column is of data type DATE, by default these columns stores data and time.(Time portion won’t be visible) So we need to remove this time portion before we put in query. The query can written like

• Select * from EMP where trunc (hiredate) = to_date (‘10/JAN/1970’, ‘DD-MM-YYYY’);
• Select * from EMP where to_char(hiredate, ‘DD-MM-YYYY’) =  ‘10/JAN/1970’;

Note: - Trunc function on Date columns removes the time portion.

40. What is different between CHAR and VARCHR2 data type?

CHAR pads spaces at the end of each string passed to it and hence memory occupied is always the length defined at the table level, while varchar2 does not holds the spaces. Say if column of width 10 then ‘vinay’ will be stored as ‘vinay     ‘in char field.

41. How do you remove the spaces across the columns?

      Using TRIM ( ) function we can remove the spaces.

Select * from EMP where TRIM (ename) =’Vinay’;

42. What is view?
43. What are different between view and table.
44. Why do we create view?
45. How do you create read only views?

Create or Replace Force View View1 as Select * From EMP with Read Only.

No DML on such views.

46. What is with check option?

 Example; - suppose we created the view like

“Create or replace view view1 Select * from EMP where deptno =10”;

 Say emp AAxx of Deptno 50 is entered to this views, it will allows us to enter the this record but when query like “select * from view1” it won’t display the employee other than deptno 10, according to the cod’s rule the data we enter into db we should be in the position view it, To incorporate such business we can have “with check option” on views, in such cases this view allow us to enter only deptno =10.

47. What is Synonyms?
48. What is sequence?
49. What is no cache option in sequence creating command?

Cache 10 will kept the next 10 sequence number in cache for faster access, it data base

Crashes these next numbers gets lost, so no cache option will be used maintain order of sequence numbers.

 

50. What is In Line view?

FROM clause in the SELECT statement will be source for data it may be table ,view , synonym or even another Query , the query written in the from clause of other query will be executed first and acts as View.

            Select * from (

                        Select   Deptno as departmentno,

                                    Dname as departmentname,

                                    Loc      as   departmentloc

                         From dept

                         Where exists (select null from dept where dept.deptno= emp.deptno)

                        )

Where departmentn0 =10;     -- where clause of outer query.

51. Can we create indexes on view?

Since views do not store data, we can’t explicitly create indexes on views, So we can create indexes on base table.

NOTE:  An empty string (‘ ‘) of length one is treated as null in Oracle, 

Assaignments

1)         How to select all the records which contains '-'in their name.

2)         What is the output of below query

         Select count (sal) from emp;

         Ename             sal

      Arun                       2000

      Bhaskar      5000

      Chandra     

      Mahesh       3000

      Rakesh                  

3) How to get below output

     Sal > 20000 then high,>=10000 then medium <10000 then low

eno       ename              high      medium            low

101       Ashok               23000   NULL                NULL

102       Bandit               NULL    NULL                7000

103       kaviram NULL    17000               NULL

104       raj                     28000   NULL                NULL

4) Similar query to delete duplicated rows

5) Employee

 eno      Name

a001     Singhal

a005     Rani

a007     Rai      

Contract

Eno            Name

P001     john

P002     paul

P004     scott

How to get below output

Eno      Ename

P001     john     

P002     paul

A001                 Singhal

A005                 Rani

6) What are the cursor attributes

7) What is the name of the pkg in PL/SQL by using which we can write a string 'Hi,it's PL/SQL' in text file

8)write a PL/SQL statement to DROP a table

9)Write the structure anonymous PL/SQL block

10)what is the value of SQL%ISOPEN

11)when a transaction ends

       a)after commit   b)after rollback c)after both  d) none

12)How to call a procedure eg:showstatus in

      a)at sql prompt

      b)Inside PL/SQL

13)How to enable Trigger

14)How to write stored function return value at runtime and how to use select statement dynamically.

15)What is the output of below PL/SQL block

declare

 v number;

Begin

Select dummy from v where 1=2

Exception

If(%notfound) then

Dbms_output.putline ("no data man");

If (other) then

Dbms_output.putline ("others");

16)what is Argument mode….???

    Create or replace function f1(x {argument mode},y {argument mode}) return Number Is

Declare

----

----

Begin

 ----

  ---

END

18) How to declare a function which will return TRUE or FALSE value

Eg)

      If (condition)

       Return TRUE

Else

      Return FALSE

19)In PL/SQL which procedure we will use to generate Customized Error Messages

a)SQLERR b)DBMS_DDL c)DBMS_DML d)……….

20) Employee

   eno    sno       enmae              sal

 Here eno=sno means both contains same values

Then which of the below statement is correct

1)select * from emp where eno>10 is efficient

2) select * from emp where sno>10 is efficient

4)both are equally efficient

5)Both are unefficient

21)A developer wants to design employee_name datatype as same lastname of employee table then which is correct??

a)emp.lastnme%type  b) emp.lastnmae%rowtype  c)….

22) The keywords new and Old are availabe for which type of triggers

a)Statement&Row level  b)Row level  c)Statement level d) none

23)What is the procedure name which can encrypts PL/SQL source code.

24)what is used in Oracle for Dynamic data replication.

25) which commands are used for import and Export data in Oracle

26)what are the minimum roles needs to assigned for  basic oracle user

27)Write Oracle hint which forces full table scan?

28)How to give read only permission for the table sales for the uers u1 and u2

29)In employee table there is an index for ename then the below sql statement

     will use the index r not

select (trim(ename.'')) from emp;

1. What are SQLCODE and SQLERRM and why are they important for PL/SQL developers?
2. what is sequence and why it is used?
3. give the syntax for creating sequence?
4. what are currval and nextval?
5. why synonyms are used?
6. what is the difference between private and public synonym?
7. what is spool file? How you create it?
8. while loading large amount of data , constraints disabled. can enabling possible if records with invalid data is present?
9. a table emp is existing with records, I want to create a table emp_temp having same structure and no data. How to do this?
10. I have a table emp having ename column which is varchar2(60). There is data in it. I need to change from varchar2(60) to varchar2(20), how to do?
11. difference between rownum and rowid?
12. select * from employee where rownum>2;  what is the output?
13. difference between RBO and CBO?
14. question on hints?
15. give a select statement to get the alternate records?  In emp table I want 1, 3,5 …… records.
16. create sequence my_seq start with 1 increment by 1; 

      select my_seq.currval from dual; what is the output of this?

17. what is autonomous transaction?

PL/SQL FAQ’S for Oracle, DBA, Developer Candidates:

1. Describe the difference between a procedure, function and anonymous pl/sql block.

Level: Low

Expected answer : Candidate should mention use of DECLARE statement, a function must return a value while a procedure doesn?t have to.

2. What is a mutating table error and how can you get around it?
Level: Intermediate
Expected answer: This happens with triggers. It occurs because the trigger is trying to update a row it is currently using. The usual fix involves either use of views or temporary tables so the database is selecting from one while updating the other.
3. Describe the use of %ROWTYPE and %TYPE in PL/SQL
Level: Low
Expected answer: %ROWTYPE allows you to associate a variable with an entire table row. The %TYPE associates a variable with a single column type.
4. What packages (if any) has Oracle provided for use by developers?
Level: Intermediate to high
Expected answer: Oracle provides the DBMS_ series of packages. There are many which developers should be aware of such as DBMS_SQL, DBMS_PIPE, DBMS_TRANSACTION, DBMS_LOCK, DBMS_ALERT, DBMS_OUTPUT, DBMS_JOB, DBMS_UTILITY, DBMS_DDL, UTL_FILE. If they can mention a few of these and describe how they used them, even better. If they include the SQL routines provided by Oracle, great, but not really what was asked.
5. Describe the use of PL/SQL tables
Level: Intermediate
Expected answer: PL/SQL tables are scalar arrays that can be referenced by a binary integer. They can be used to hold values for use in later queries or calculations. In Oracle 8 they will be able to be of the %ROWTYPE designation, or RECORD.
6. When is a declare statement needed ?
Level: Low
The DECLARE statement is used in PL/SQL anonymous blocks such as with stand alone, non-stored PL/SQL procedures. It must come first in a PL/SQL stand alone file if it is used.
7. In what order should a open/fetch/loop set of commands in a PL/SQL block be implemented if you use the %NOTFOUND cursor variable in the exit when statement? Why?
Level: Intermediate
Expected answer: OPEN then FETCH then LOOP followed by the exit when. If not specified in this order will result in the final return being done twice because of the way the %NOTFOUND is handled by PL/SQL.
8. What are SQLCODE and SQLERRM and why are they important for PL/SQL developers?
Level: Intermediate
Expected answer: SQLCODE returns the value of the error number for the last error encountered. The SQLERRM returns the actual error message for the last error encountered. They can be used in exception handling to report, or, store in an error log table, the error that occurred in the code. These are especially useful for the WHEN OTHERS exception.
9. How can you find within a PL/SQL block, if a cursor is open?
Level: Low
Expected answer: Use the %ISOPEN cursor status variable.
10. How can you generate debugging output from PL/SQL?
Level:Intermediate to high
Expected answer: Use the DBMS_OUTPUT package. Another possible method is to just use the SHOW ERROR command, but this only shows errors. The DBMS_OUTPUT package can be used to show intermediate results from loops and the status of variables as the procedure is executed. The new package UTL_FILE can also be used.
11. What are the types of triggers?
Level:Intermediate to high
Expected Answer: There are 12 types of triggers in PL/SQL that consist of combinations of the BEFORE, AFTER, ROW, TABLE, INSERT, UPDATE, DELETE and ALL key words:
BEFORE ALL ROW INSERT
AFTER ALL ROW INSERT
BEFORE INSERT
AFTER INSERT etc.



                                                            DBA:
1. Give one method for transferring a table from one schema to another:
Level:Intermediate
Expected Answer: There are several possible methods, export-import, CREATE TABLE... AS SELECT, or COPY.
2. What is the purpose of the IMPORT option IGNORE? What is it?s default setting?
Level: Low
Expected Answer: The IMPORT IGNORE option tells import to ignore "already exists" errors. If it is not specified the tables that already exist will be skipped. If it is specified, the error is ignored and the tables data will be inserted. The default value is N.
3. You have a rollback segment in a version 7.2 database that has expanded beyond optimal, how can it be restored to optimal?
Level: Low
Expected answer: Use the ALTER TABLESPACE ..... SHRINK command.
4. If the DEFAULT and TEMPORARY tablespace clauses are left out of a CREATE USER command what happens? Is this bad or good? Why?
Level: Low
Expected answer: The user is assigned the SYSTEM tablespace as a default and temporary tablespace. This is bad because it causes user objects and temporary segments to be placed into the SYSTEM tablespace resulting in fragmentation and improper table placement (only data dictionary objects and the system rollback segment should be in SYSTEM).
5. What are some of the Oracle provided packages that DBAs should be aware of?
Level: Intermediate to High
Expected answer: Oracle provides a number of packages in the form of the DBMS_ packages owned by the SYS user. The packages used by DBAs may include: DBMS_SHARED_POOL, DBMS_UTILITY, DBMS_SQL, DBMS_DDL, DBMS_SESSION, DBMS_OUTPUT and DBMS_SNAPSHOT. They may also try to answer with the UTL*.SQL or CAT*.SQL series of SQL procedures. These can be viewed as extra credit but aren?t part of the answer.
6. What happens if the constraint name is left out of a constraint clause?
Level: Low
Expected answer: The Oracle system will use the default name of SYS_Cxxxx where xxxx is a system generated number. This is bad since it makes tracking which table the constraint belongs to or what the constraint does harder.
7. What happens if a tablespace clause is left off of a primary key constraint clause?
Level: Low
Expected answer: This results in the index that is automatically generated being placed in then users default tablespace. Since this will usually be the same tablespace as the table is being created in, this can cause serious performance problems.
8. What is the proper method for disabling and re-enabling a primary key constraint?
Level: Intermediate
Expected answer: You use the ALTER TABLE command for both. However, for the enable clause you must specify the USING INDEX and TABLESPACE clause for primary keys.
9. What happens if a primary key constraint is disabled and then enabled without fully specifying the index clause?
Level: Intermediate
Expected answer: The index is created in the user?s default tablespace and all sizing information is lost. Oracle doesn?t store this information as a part of the constraint definition, but only as part of the index definition, when the constraint was disabled the index was dropped and the information is gone.
10. (On UNIX) When should more than one DB writer process be used? How many should be used?
Level: High
Expected answer: If the UNIX system being used is capable of asynchronous IO then only one is required, if the system is not capable of asynchronous IO then up to twice the number of disks used by Oracle number of DB writers should be specified by use of the db_writers initialization parameter.
11. You are using hot backup without being in archivelog mode, can you recover in the event of a failure? Why or why not?
Level: High
Expected answer: You can?t use hot backup without being in archivelog mode. So no, you couldn?t recover.
12. What causes the "snapshot too old" error? How can this be prevented or mitigated?
Level: Intermediate
Expected answer: This is caused by large or long running transactions that have either wrapped onto their own rollback space or have had another transaction write on part of their rollback space. This can be prevented or mitigated by breaking the transaction into a set of smaller transactions or increasing the size of the rollback segments and their extents.
13. How can you tell if a database object is invalid?
Level: Low
Expected answer: By checking the status column of the DBA_, ALL_ or USER_OBJECTS views, depending upon whether you own or only have permission on the view or are using a DBA account.
14. A user is getting an ORA-00942 error yet you know you have granted them permission on the table, what else should you check?
Level: Low
Expected answer: You need to check that the user has specified the full name of the object (select empid from scott.emp; instead of select empid from emp;) or has a synonym that points to the object (create synonym emp for scott.emp;)
15. A developer is trying to create a view and the database won?t let him. He has the "DEVELOPER" role which has the "CREATE VIEW" system privilege and SELECT grants on the tables he is using, what is the problem?
Level: Intermediate
Expected answer: You need to verify the developer has direct grants on all tables used in the view. You can?t create a stored object with grants given through views.
16. If you have an example table, what is the best way to get sizing data for the production table implementation?
Level: Intermediate
Expected answer: The best way is to analyze the table and then use the data provided in the DBA_TABLES view to get the average row length and other pertinent data for the calculation. The quick and dirty way is to look at the number of blocks the table is actually using and ratio the number of rows in the table to its number of blocks against the number of expected rows.
17. How can you find out how many users are currently logged into the database? How can you find their operating system id?
Level: high
Expected answer: There are several ways. One is to look at the v$session or v$process views. Another way is to check the current_logins parameter in the v$sysstat view. Another if you are on UNIX is to do a "ps -ef|grep oracle|wc -l? command, but this only works against a single instance installation.
18. A user selects from a sequence and gets back two values, his select is:
SELECT pk_seq.nextval FROM dual;
What is the problem?
Level: Intermediate
Expected answer: Somehow two values have been inserted into the dual table. This table is a single row, single column table that should only have one value in it.
19. How can you determine if an index needs to be dropped and rebuilt?
Level: Intermediate
Expected answer: Run the ANALYZE INDEX command on the index to validate its structure and then calculate the ratio of LF_BLK_LEN/LF_BLK_LEN+BR_BLK_LEN and if it isn?t near 1.0 (i.e. greater than 0.7 or so) then the index should be rebuilt. Or if the ratio
BR_BLK_LEN/ LF_BLK_LEN+BR_BLK_LEN is nearing 0.3.
SQL/ SQLPlus
1. How can variables be passed to a SQL routine?
Level: Low
Expected answer: By use of the & symbol. For passing in variables the numbers 1-8 can be used (&1, &2,...,&8) to pass the values after the command into the SQLPLUS session. To be prompted for a specific variable, place the ampersanded variable in the code itself:
"select * from dba_tables where owner=&owner_name;" . Use of double ampersands tells SQLPLUS to resubstitute the value for each subsequent use of the variable, a single ampersand will cause a reprompt for the value unless an ACCEPT statement is used to get the value from the user.
2. You want to include a carriage return/linefeed in your output from a SQL script, how can you do this?
Level: Intermediate to high
Expected answer: The best method is to use the CHR() function (CHR(10) is a return/linefeed) and the concatenation function "||". Another method, although it is hard to document and isn?t always portable is to use the return/linefeed as a part of a quoted string.
3. How can you call a PL/SQL procedure from SQL?
Level: Intermediate
Expected answer: By use of the EXECUTE (short form EXEC) command.
4. How do you execute a host operating system command from within SQL?
Level: Low
Expected answer: By use of the exclamation point "!" (in UNIX and some other OS) or the HOST (HO) command.
5. You want to use SQL to build SQL, what is this called and give an example
Level: Intermediate to high
Expected answer: This is called dynamic SQL. An example would be:
set lines 90 pages 0 termout off feedback off verify off
spool drop_all.sql
select ?drop user ?||username||? cascade;? from dba_users
where username not in ("SYS?,?SYSTEM?);
spool off
Essentially you are looking to see that they know to include a command (in this case DROP USER...CASCADE;) and that you need to concatenate using the ?||? the values selected from the database.
6. What SQLPlus command is used to format output from a select?
Level: low
Expected answer: This is best done with the COLUMN command.
7. You want to group the following set of select returns, what can you group on?
Max(sum_of_cost), min(sum_of_cost), count(item_no), item_no
Level: Intermediate
Expected answer: The only column that can be grouped on is the "item_no" column, the rest have aggregate functions associated with them.
8. What special Oracle feature allows you to specify how the cost based system treats a SQL statement?
Level: Intermediate to high
Expected answer: The COST based system allows the use of HINTs to control the optimizer path selection. If they can give some example hints such as FIRST ROWS, ALL ROWS, USING INDEX, STAR, even better.
9. You want to determine the location of identical rows in a table before attempting to place a unique index on the table, how can this be done?
Level: High
Expected answer: Oracle tables always have one guaranteed unique column, the rowid column. If you use a min/max function against your rowid and then select against the proposed primary key you can squeeze out the rowids of the duplicate rows pretty quick. For example:
select rowid from emp e
where e.rowid > (select min(x.rowid)
from emp x
where x.emp_no = e.emp_no);
In the situation where multiple columns make up the proposed key, they must all be used in the where clause.
10. What is a Cartesian product?
Level: Low
Expected answer: A Cartesian product is the result of an unrestricted join of two or more tables. The result set of a three table Cartesian product will have x * y * z number of rows where x, y, z correspond to the number of rows in each table involved in the join.
11. You are joining a local and a remote table, the network manager complains about the traffic involved, how can you reduce the network traffic?
Level: High
Expected answer: Push the processing of the remote data to the remote instance by using a view to pre-select the information for the join. This will result in only the data required for the join being sent across.
12. What is the default ordering of an ORDER BY clause in a SELECT statement?
Level: Low
Expected answer: Ascending
13. What is tkprof and how is it used?
Level: Intermediate to high
Expected answer: The tkprof tool is a tuning tool used to determine cpu and execution times for SQL statements. You use it by first setting timed_statistics to true in the initialization file and then turning on tracing for either the entire database via the sql_trace parameter or for the session using the ALTER SESSION command. Once the trace file is generated you run the tkprof tool against the trace file and then look at the output from the tkprof tool. This can also be used to generate explain plan output.
14. What is explain plan and how is it used?
Level: Intermediate to high
Expected answer: The EXPLAIN PLAN command is a tool to tune SQL statements. To use it you must have an explain_table generated in the user you are running the explain plan for. This is created using the utlxplan.sql script. Once the explain plan table exists you run the explain plan command giving as its argument the SQL statement to be explained. The explain_plan table is then queried to see the execution plan of the statement. Explain plans can also be run using tkprof.
15. How do you set the number of lines on a page of output? The width?
Level: Low
Expected answer: The SET command in SQLPLUS is used to control the number of lines generated per page and the width of those lines, for example SET PAGESIZE 60 LINESIZE 80 will generate reports that are 60 lines long with a line width of 80 characters. The PAGESIZE and LINESIZE options can be shortened to PAGES and LINES.
16. How do you prevent output from coming to the screen?
Level: Low
Expected answer: The SET option TERMOUT controls output to the screen. Setting TERMOUT OFF turns off screen output. This option can be shortened to TERM.
17. How do you prevent Oracle from giving you informational messages during and after a SQL statement execution?
Level: Low
Expected answer: The SET options FEEDBACK and VERIFY can be set to OFF.
18. How do you generate file output from SQL?
Level: Low
Expected answer: By use of the SPOOL command
                                                Tuning Questions:
1. A tablespace has a table with 30 extents in it. Is this bad? Why or why not.
Level: Intermediate
Expected answer: Multiple extents in and of themselves aren?t bad. However if you also have chained rows this can hurt performance.
2. How do you set up tablespaces during an Oracle installation?
Level: Low
Expected answer: You should always attempt to use the Oracle Flexible Architecture standard or another partitioning scheme to ensure proper separation of SYSTEM, ROLLBACK, REDO LOG, DATA, TEMPORARY and INDEX segments.
3. You see multiple fragments in the SYSTEM tablespace, what should you check first?
Level: Low
Expected answer: Ensure that users don?t have the SYSTEM tablespace as their TEMPORARY or DEFAULT tablespace assignment by checking the DBA_USERS view.
4. What are some indications that you need to increase the SHARED_POOL_SIZE parameter?
Level: Intermediate
Expected answer: Poor data dictionary or library cache hit ratios, getting error ORA-04031. Another indication is steadily decreasing performance with all other tuning parameters the same.
5. What is the general guideline for sizing db_block_size and db_multi_block_read for an application that does many full table scans?
Level: High
Expected answer: Oracle almost always reads in 64k chunks. The two should have a product equal to 64 or a multiple of 64.
6. What is the fastest query method for a table?
Level: Intermediate
Expected answer: Fetch by rowid
7. Explain the use of TKPROF? What initialization parameter should be turned on to get full TKPROF output?
Level: High
Expected answer: The tkprof tool is a tuning tool used to determine cpu and execution times for SQL statements. You use it by first setting timed_statistics to true in the initialization file and then turning on tracing for either the entire database via the sql_trace parameter or for the session using the ALTER SESSION command. Once the trace file is generated you run the tkprof tool against the trace file and then look at the output from the tkprof tool. This can also be used to generate explain plan output.
8. When looking at v$sysstat you see that sorts (disk) is high. Is this bad or good? If bad -How do you correct it?
Level: Intermediate
Expected answer: If you get excessive disk sorts this is bad. This indicates you need to tune the sort area parameters in the initialization files. The major sort are parameter is the SORT_AREA_SIZe parameter.

9. When should you increase copy latches? What parameters control copy latches?
Level: high
Expected answer: When you get excessive contention for the copy latches as shown by the "redo copy" latch hit ratio. You can increase copy latches via the initialization parameter LOG_SIMULTANEOUS_COPIES to twice the number of CPUs on your system.
10. Where can you get a list of all initialization parameters for your instance? How about an indication if they are default settings or have been changed?
Level: Low
Expected answer: You can look in the init.ora file for an indication of manually set parameters. For all parameters, their value and whether or not the current value is the default value, look in the v$parameter view.
11. Describe hit ratio as it pertains to the database buffers. What is the difference between instantaneous and cumulative hit ratio and which should be used for tuning?
Level: Intermediate
Expected answer: The hit ratio is a measure of how many times the database was able to read a value from the buffers verses how many times it had to re-read a data value from the disks. A value greater than 80-90% is good, less could indicate problems. If you simply take the ratio of existing parameters this will be a cumulative value since the database started. If you do a comparison between pairs of readings based on some arbitrary time span, this is the instantaneous ratio for that time span. Generally speaking an instantaneous reading gives more valuable data since it will tell you what your instance is doing for the time it was generated over.
12. Discuss row chaining, how does it happen? How can you reduce it? How do you correct it?
Level: high
Expected answer: Row chaining occurs when a VARCHAR2 value is updated and the length of the new value is longer than the old value and won?t fit in the remaining block space. This results in the row chaining to another block. It can be reduced by setting the storage parameters on the table to appropriate values. It can be corrected by export and import of the effected table.
13. When looking at the estat events report you see that you are getting busy buffer waits. Is this bad? How can you find what is causing it?
Level: high
Expected answer: Buffer busy waits could indicate contention in redo, rollback or data blocks. You need to check the v$waitstat view to see what areas are causing the problem. The value of the "count" column tells where the problem is, the "class" column tells you with what. UNDO is rollback segments, DATA is data base buffers.

14. If you see contention for library caches how can you fix it?
Level: Intermediate
Expected answer: Increase the size of the shared pool.
15. If you see statistics that deal with "undo" what are they really talking about?
Level: Intermediate
Expected answer: Rollback segments and associated structures.
16. If a tablespace has a default pctincrease of zero what will this cause (in relationship to the smon process)?
Level: High
Expected answer: The SMON process won?t automatically coalesce its free space fragments.
17. If a tablespace shows excessive fragmentation what are some methods to defragment the tablespace? (7.1,7.2 and 7.3 only)
Level: High
Expected answer: In Oracle 7.0 to 7.2 The use of the 'alter session set events 'immediate trace name coalesce level ts#';? command is the easiest way to defragment contiguous free space fragmentation. The ts# parameter corresponds to the ts# value found in the ts$ SYS table. In version 7.3 the ?alter tablespace coalesce;? is best. If the free space isn?t contiguous then export, drop and import of the tablespace contents may be the only way to reclaim non-contiguous free space.
18. How can you tell if a tablespace has excessive fragmentation?
Level: Intermediate
If a select against the dba_free_space table shows that the count of a tablespaces extents is greater than the count of its data files, then it is fragmented.
19. You see the following on a status report:
redo log space requests 23
redo log space wait time 0
Is this something to worry about? What if redo log space wait time is high? How can you fix this?
Level: Intermediate
Expected answer: Since the wait time is zero, no. If the wait time was high it might indicate a need for more or larger redo logs.
20. What can cause a high value for recursive calls? How can this be fixed?
Level: High
Expected answer: A high value for recursive calls is cause by improper cursor usage, excessive dynamic space management actions, and or excessive statement re-parses. You need to determine the cause and correct it By either relinking applications to hold cursors, use proper space management techniques (proper storage and sizing) or ensure repeat queries are placed in packages for proper reuse.
21. If you see a pin hit ratio of less than 0.8 in the estat library cache report is this a problem? If so, how do you fix it?
Level: Intermediate
Expected answer: This indicate that the shared pool may be too small. Increase the shared pool size.
22. If you see the value for reloads is high in the estat library cache report is this a matter for concern?
Level: Intermediate
Expected answer: Yes, you should strive for zero reloads if possible. If you see excessive reloads then increase the size of the shared pool.
23. You look at the dba_rollback_segs view and see that there is a large number of shrinks and they are of relatively small size, is this a problem? How can it be fixed if it is a problem?
Level: High
Expected answer: A large number of small shrinks indicates a need to increase the size of the rollback segment extents. Ideally you should have no shrinks or a small number of large shrinks. To fix this just increase the size of the extents and adjust optimal accordingly.
24. You look at the dba_rollback_segs view and see that you have a large number of wraps is this a problem?
Level: High
Expected answer: A large number of wraps indicates that your extent size for your rollback segments are probably too small. Increase the size of your extents to reduce the number of wraps. You can look at the average transaction size in the same view to get the information on transaction size.



25. In a system with an average of 40 concurrent users you get the following from a query on rollback extents:
ROLLBACK CUR EXTENTS
--------------------- --------------------------
R01 11
R02 8
R03 12
R04 9
SYSTEM 4
You have room for each to grow by 20 more extents each. Is there a problem? Should you take any action?
Level: Intermediate
Expected answer: No there is not a problem. You have 40 extents showing and an average of 40 concurrent users. Since there is plenty of room to grow no action is needed.
26. You see multiple extents in the temporary tablespace. Is this a problem?
Level: Intermediate
Expected answer: As long as they are all the same size this isn?t a problem. In fact, it can even improve performance since Oracle won?t have to create a new extent when a user needs one.
Installation/Configuration
1. Define OFA.
Level: Low
Expected answer: OFA stands for Optimal Flexible Architecture. It is a method of placing directories and files in an Oracle system so that you get the maximum flexibility for future tuning and file placement.
2. How do you set up your tablespace on installation?
Level: Low
Expected answer: The answer here should show an understanding of separation of redo and rollback, data and indexes and isolation os SYSTEM tables from other tables. An example would be to specify that at least 7 disks should be used for an Oracle installation so that you can place SYSTEM tablespace on one, redo logs on two (mirrored redo logs) the TEMPORARY tablespace on another, ROLLBACK tablespace on another and still have two for DATA and INDEXES. They should indicate how they will handle archive logs and exports as well. As long as they have a logical plan for combining or further separation more or less disks can be specified.
3. What should be done prior to installing Oracle (for the OS and the disks)?
Level: Low
Expected Answer: adjust kernel parameters or OS tuning parameters in accordance with installation guide. Be sure enough contiguous disk space is available.
4. You have installed Oracle and you are now setting up the actual instance. You have been waiting an hour for the initialization script to finish, what should you check first to determine if there is a problem?
Level: Intermediate to high
Expected Answer: Check to make sure that the archiver isn?t stuck. If archive logging is turned on during install a large number of logs will be created. This can fill up your archive log destination causing Oracle to stop to wait for more space.
5. When configuring SQLNET on the server what files must be set up?
Level: Intermediate
Expected answer: INITIALIZATION file, TNSNAMES.ORA file, SQLNET.ORA file
6. When configuring SQLNET on the client what files need to be set up?
Level: Intermediate
Expected answer: SQLNET.ORA, TNSNAMES.ORA
7. What must be installed with ODBC on the client in order for it to work with Oracle?
Level: Intermediate
Expected answer: SQLNET and PROTOCOL (for example: TCPIP adapter) layers of the transport programs.
8. You have just started a new instance with a large SGA on a busy existing server. Performance is terrible, what should you check for?
Level: Intermediate
Expected answer: The first thing to check with a large SGA is that it isn?t being swapped out.
9. What OS user should be used for the first part of an Oracle installation (on UNIX)?
Level: low
Expected answer: You must use root first.
10. When should the default values for Oracle initialization parameters be used as is?
Level: Low
Expected answer: Never
11. How many control files should you have? Where should they be located?
Level: Low
Expected answer: At least 2 on separate disk spindles. Be sure they say on separate disks, not just file systems.
12. How many redo logs should you have and how should they be configured for maximum recoverability?
Level: Intermediate
Expected answer: You should have at least three groups of two redo logs with the two logs each on a separate disk spindle (mirrored by Oracle). The redo logs should not be on raw devices on UNIX if it can be avoided.
13. You have a simple application with no "hot" tables (i.e. uniform IO and access requirements). How many disks should you have assuming standard layout for SYSTEM, USER, TEMP and ROLLBACK tablespaces?
Expected answer: At least 7, see disk configuration answer above.
Data Modeler:
1. Describe third normal form?
Level: Low
Expected answer: Something like: In third normal form all attributes in an entity are related to the primary key and only to the primary key
2. Is the following statement true or false:
"All relational databases must be in third normal form"
Why or why not?
Level: Intermediate
Expected answer: False. While 3NF is good for logical design most databases, if they have more than just a few tables, will not perform well using full 3NF. Usually some entities will be denormalized in the logical to physical transfer process.
3. What is an ERD?
Level: Low
Expected answer: An ERD is an Entity-Relationship-Diagram. It is used to show the entities and relationships for a database logical model.
4. Why are recursive relationships bad? How do you resolve them?
Level: Intermediate
A recursive relationship (one where a table relates to itself) is bad when it is a hard relationship (i.e. neither side is a "may" both are "must") as this can result in it not being possible to put in a top or perhaps a bottom of the table (for example in the EMPLOYEE table you couldn?t put in the PRESIDENT of the company because he has no boss, or the junior janitor because he has no subordinates). These type of relationships are usually resolved by adding a small intersection entity.
5. What does a hard one-to-one relationship mean (one where the relationship on both ends is "must")?
Level: Low to intermediate
Expected answer: This means the two entities should probably be made into one entity.
6. How should a many-to-many relationship be handled?
Level: Intermediate
Expected answer: By adding an intersection entity table
7. What is an artificial (derived) primary key? When should an artificial (or derived) primary key be used?
Level: Intermediate
Expected answer: A derived key comes from a sequence. Usually it is used when a concatenated key becomes too cumbersome to use as a foreign key.
8. When should you consider denormalization?
Level: Intermediate
Expected answer: Whenever performance analysis indicates it would be beneficial to do so without compromising data integrity.
UNIX:
1. How can you determine the space left in a file system?
Level: Low
Expected answer: There are several commands to do this: du, df, or bdf
2. How can you determine the number of SQLNET users logged in to the UNIX system?
Level: Intermediate
Expected answer: SQLNET users will show up with a process unique name that begins with oracle, if you do a ps -ef|grep oracle|wc -l you can get a count of the number of users.
3. What command is used to type files to the screen?
Level: Low
Expected answer: cat, more, pg
4. What command is used to remove a file?
Level: Low
Expected answer: rm
5. Can you remove an open file under UNIX?
Level: Low
Expected answer: yes
6. How do you create a decision tree in a shell script?
Level: intermediate
Expected answer: depending on shell, usually a case-esac or an if-endif or fi structure
7. What is the purpose of the grep command?
Level: Low
Expected answer: grep is a string search command that parses the specified string from the specified file or files
8. The system has a program that always includes the word nocomp in its name, how can you determine the number of processes that are using this program?
Level: intermediate
Expected answer: ps -ef|grep *nocomp*|wc -l
9. What is an inode?
Level: Intermediate
Expected answer: an inode is a file status indicator. It is stored in both disk and memory and tracts file status. There is one inode for each file on the system.
10. The system administrator tells you that the system hasn?t been rebooted in 6 months, should he be proud of this?
Level: High
Expected answer: Maybe. Some UNIX systems don?t clean up well after themselves. Inode problems and dead user processes can accumulate causing possible performance and corruption problems. Most UNIX systems should have a scheduled periodic reboot so file systems can be checked and cleaned and dead or zombie processes cleared out.
11. What is redirection and how is it used?
Level: Intermediate
Expected answer: redirection is the process by which input or output to or from a process is redirected to another process. This can be done using the pipe symbol "|", the greater than symbol ">" or the "tee" command. This is one of the strengths of UNIX allowing the output from one command to be redirected directly into the input of another command.
12. How can you find dead processes?
Level: Intermediate
Expected answer: ps -ef|grep zombie -- or -- who -d depending on the system.
13. How can you find all the processes on your system?
Level: Low
Expected answer: Use the ps command
14. How can you find your id on a system?
Level: Low
Expected answer: Use the "who am i" command.
15. What is the finger command?
Level: Low
Expected answer: The finger command uses data in the passwd file to give information on system users.
16. What is the easiest method to create a file on UNIX?
Level: Low
Expected answer: Use the touch command
17. What does >> do?
Level: Intermediate
Expected answer: The ">>" redirection symbol appends the output from the command specified into the file specified. The file must already have been created.
18. If you aren?t sure what command does a particular UNIX function what is the best way to determine the command?
Expected answer: The UNIX man -k command will search the man pages for the value specified. Review the results from the command to find the command of interest.
Oracle Troubleshooting:
1. How can you determine if an Oracle instance is up from the operating system level?
Level: Low
Expected answer: There are several base Oracle processes that will be running on multi-user operating systems, these will be smon, pmon, dbwr and lgwr. Any answer that has them using their operating system process showing feature to check for these is acceptable. For example, on UNIX a ps -ef|grep dbwr will show what instances are up.
2. Users from the PC clients are getting messages indicating :
Level: Low
ORA-06114: (Cnct err, can't get err txt. See Servr Msgs & Codes Manual)
What could the problem be?
Expected answer: The instance name is probably incorrect in their connection string.
3. Users from the PC clients are getting the following error stack:
Level: Low
ERROR: ORA-01034: ORACLE not available
ORA-07318: smsget: open error when opening sgadef.dbf file.
HP-UX Error: 2: No such file or directory
What is the probable cause?
Expected answer: The Oracle instance is shutdown that they are trying to access, restart the instance.
4. How can you determine if the SQLNET process is running for SQLNET V1? How about V2?
Level: Low
Expected answer: For SQLNET V1 check for the existence of the orasrv process. You can use the command "tcpctl status" to get a full status of the V1 TCPIP server, other protocols have similar command formats. For SQLNET V2 check for the presence of the LISTENER process(s) or you can issue the command "lsnrctl status".
5. What file will give you Oracle instance status information? Where is it located?
Level: Low
Expected answer: The alert.ora log. It is located in the directory specified by the background_dump_dest parameter in the v$parameter table.
6. Users aren?t being allowed on the system. The following message is received:
Level: Intermediate
ORA-00257 archiver is stuck. Connect internal only, until freed
What is the problem?
Expected answer: The archive destination is probably full, backup the archive logs and remove them and the archiver will re-start.
7. Where would you look to find out if a redo log was corrupted assuming you are using Oracle mirrored redo logs?
Level: Intermediate
Expected answer: There is no message that comes to the SQLDBA or SRVMGR programs during startup in this situation, you must check the alert.log file for this information.
8. You attempt to add a datafile and get:
Level: Intermediate
ORA-01118: cannot add anymore datafiles: limit of 40 exceeded
What is the problem and how can you fix it?
Expected answer: When the database was created the db_files parameter in the initialization file was set to 40. You can shutdown and reset this to a higher value, up to the value of MAX_DATAFILES as specified at database creation. If the MAX_DATAFILES is set to low, you will have to rebuild the control file to increase it before proceeding.
9. You look at your fragmentation report and see that smon hasn?t coalesced any of you tablespaces, even though you know several have large chunks of contiguous free extents. What is the problem?
Level: High
Expected answer: Check the dba_tablespaces view for the value of pct_increase for the tablespaces. If pct_increase is zero, smon will not coalesce their free space.
10. Your users get the following error:
Level: Intermediate
ORA-00055 maximum number of DML locks exceeded
What is the problem and how do you fix it?
Expected answer: The number of DML Locks is set by the initialization parameter DML_LOCKS. If this value is set to low (which it is by default) you will get this error. Increase the value of DML_LOCKS. If you are sure that this is just a temporary problem, you can have them wait and then try again later and the error should clear.
11. You get a call from you backup DBA while you are on vacation. He has corrupted all of the control files while playing with the ALTER DATABASE BACKUP CONTROLFILE command. What do you do?
Level: High
Expected answer: As long as all datafiles are safe and he was successful with the BACKUP controlfile command you can do the following:
CONNECT INTERNAL
STARTUP MOUNT
(Take any read-only tablespaces offline before next step ALTER DATABASE DATAFILE .... OFFLINE;)
RECOVER DATABASE USING BACKUP CONTROLFILE
ALTER DATABASE OPEN RESETLOGS;
(bring read-only tablespaces back online)
Shutdown and backup the system, then restart
If they have a recent output file from the ALTER DATABASE BACKUP CONTROL FILE TO TRACE; command, they can use that to recover as well.
If no backup of the control file is available then the following will be required:
CONNECT INTERNAL
STARTUP NOMOUNT
CREATE CONTROL FILE .....;
However, they will need to know all of the datafiles, logfiles, and settings for MAXLOGFILES, MAXLOGMEMBERS, MAXLOGHISTORY, MAXDATAFILES for the database to use the command.

1. give the full select statement syntax including group by and having clause.
2. select ….

.

.

.

group by

having

     select ….

.

.

.

having

group by

Both are correct or which one of the two is wrong.

3. difference between truncate and delete?

4. How to find the constraints on a particular table?

5. what is referential integrity

6. Where can information of indexes can be fetched from?

7. how can you find the status of a particular object in database? Which data dictionary table can be used ?

8. Give the reasoning behind using an index.

9. What are the different type indexes?

10. how to disable a constraint ? give the full syntax?

11. if you need to drop all the tables in a schema then how to do that?

12. What is mutating trigger?

13. What are the 2 implicit cursors used in triggers which are exclusive for triggers only? (ans. :New and :old)

14. Give the full syntax for creating a view?

15. what is instead of trigger?

16. what are the different type of triggers?

17. can mutating trigger appear on statement level trigger?

18. Can commit/rollback happen in triggers?

19. What are savepoints and how are they used? Give the syntax.

20. Why do you use exception? What is the purpose?

21. What are the different type of exceptions?

22. What is pragma exception init and why is it used?

23. give the full syntax of declaring user defined exception and how to raise it.

24. how to delete the duplicate records in a table.

25. the emp table has gender column. Give a select statement that will give the count of male and female. One select statement only?

26. difference between union and union all?

27. how to find out all those tables which are having a column say deptno?

28. Explain the difference between a FUNCTION, PROCEDURE and PACKAGE.

29. difference between in, in out and out parameters. Can you use out and in out parameters in a function?

30. what is private and public.

31. can you have procedures in the package body without having it in specification?

32. can you have the procedure declaration in the package specification without having it in the package body?

33. what is autonomous transaction?

34. what are explicit cursors and implicit cursors?

35. delete from emp; is this implicit cursor or explicit cursor?

36. select empno into :empno from emp where empno=100; is this implicit or explicit curs

37. give the cursor attributes for both explicit and implicit cursors?

38. write the for loop cursor syntax

39. what is parametrized cursors? Give the syntax?

40. can you use array in plsql?

41.  What is a PL/SQL collection? PL/SQL Table, Varray, PL/SQL Array, etc and uses?

42. give the syntax of plsql table. Write the various functions used by the plsql table.

43. can you call a function in sql statement? Can you call a procedure in a sql statement? Give reason?

44. difference between for loop and while loop

45. what is correlated subquery?

46. difference between in and exists?

47. a table emp with columns empno and ename is existing. Want to add a new column deptno number(4) in this table.

How to do this? Give the full syntax?

48. Why is the Connect-by clause used ?
49. difference between substr and instr and give the syntax?
50. what are the various date functions available?
51. at max a table can have how many columns of long type?
52. where can the code of procedure be fetched from?
53. what is the difference between drop procedure and create or replace procedure?
54. what is the advantages of using packages?
55. why nvl is used?
56. what is a plsql block and give the syntax?
57. how can a procedure or package or function executed from the sql statement.
58. difference between to_date and to_char functions?

SQL

1.  Which is the subset of SQL commands used to manipulate Oracle Database structures, including tables?

Data Definition Language (DDL)

2.      What operator performs pattern matching?

LIKE operator

3.      What operator tests column for the absence of data?

IS NULL operator

4.      Which command executes the contents of a specified file?

             START <filename> or @<filename>

5.      What is the parameter substitution symbol used with INSERT INTO command?

             &

6.      Which command displays the SQL command in the SQL buffer, and then executes it?

             RUN

7.      What are the wildcards used for pattern matching?

             _ for single character substitution and % for multi-character substitution

8.      State true or false. EXISTS, SOME, ANY are operators in SQL.

             True

9.      State true or false. !=, <>, ^= all denote the same operation.

             True

10.  What are the privileges that can be granted on a table by a user to others?

            Insert, update, delete, select, references, index, execute, alter, all

11.  What command is used to get back the privileges offered by the GRANT command?

             REVOKE

12.  Which system tables contain information on privileges granted and privileges obtained?

             USER_TAB_PRIVS_MADE, USER_TAB_PRIVS_RECD

13.  Which system table contains information on constraints on all the tables created?

             USER_CONSTRAINTS

14.        TRUNCATE TABLE EMP;

DELETE FROM EMP;

Will the outputs of the above two commands differ?

             Both will result in deleting all the rows in the table EMP.

15.  What is the difference between TRUNCATE and DELETE commands?

             TRUNCATE is a DDL command whereas DELETE is a DML command. Hence DELETE operation can be rolled back, but TRUNCATE operation cannot be rolled back. WHERE clause can be used with DELETE and not with TRUNCATE.

16.  What command is used to create a table by copying the structure of another table?

Answer :

             CREATE TABLE .. AS SELECT command

Explanation :

To copy only the structure, the WHERE clause of the SELECT command should contain a FALSE statement as in the following.

CREATE TABLE NEWTABLE AS SELECT * FROM EXISTINGTABLE WHERE 1=2;

If the WHERE condition is true, then all the rows or rows satisfying the condition will be copied to the new table.

17.  What will be the output of the following query?

SELECT REPLACE(TRANSLATE(LTRIM(RTRIM('!! ATHEN !!','!'), '!'), 'AN', '**'),'*','TROUBLE') FROM DUAL;

             TROUBLETHETROUBLE

18.  What will be the output of the following query?

SELECT  DECODE(TRANSLATE('A','1234567890','1111111111'), '1','YES', 'NO' );

Answer :

             NO

Explanation :

The query checks whether a given string is a numerical digit.

19.  What does the following query do?

SELECT SAL + NVL(COMM,0) FROM EMP;

             This displays the total salary of all employees. The null values in the commission column will be replaced by 0 and added to salary.

20.  Which date function is used to find the difference between two dates?

             MONTHS_BETWEEN

21.  Why does the following command give a compilation error?

DROP TABLE &TABLE_NAME;

             Variable names should start with an alphabet. Here the table name starts with an '&' symbol.

22.  What is the advantage of specifying WITH GRANT OPTION in the GRANT command?

             The privilege receiver can further grant the privileges he/she has obtained from the owner to any other user.

23.  What is the use of the DROP option in the ALTER TABLE command?

             It is used to drop constraints specified on the table.

24.  What is the value of ‘comm’ and ‘sal’ after executing the following query if the initial value of ‘sal’ is 10000?

UPDATE EMP SET SAL = SAL + 1000, COMM = SAL*0.1;

             sal = 11000, comm = 1000

25.  What is the use of DESC in SQL?

Answer :

             DESC has two purposes. It is used to describe a schema as well as to retrieve rows from table in descending order.

Explanation :

The query SELECT * FROM EMP ORDER BY ENAME DESC will display the output sorted on ENAME in descending order.

26.  What is the use of CASCADE CONSTRAINTS?

             When this clause is used with the DROP command, a parent table can be dropped even when a child table exists.

27.  Which function is used to find the largest integer less than or equal to a specific value?

             FLOOR

28.  What is the output of the following query?

SELECT TRUNC(1234.5678,-2) FROM DUAL;

             1200

SQL – QUERIES

I. SCHEMAS

Table 1 : STUDIES

PNAME  (VARCHAR),  SPLACE (VARCHAR),  COURSE (VARCHAR),  CCOST (NUMBER)

Table 2 : SOFTWARE

PNAME (VARCHAR), TITLE (VARCHAR), DEVIN (VARCHAR), SCOST (NUMBER), DCOST (NUMBER), SOLD (NUMBER)

Table 3 : PROGRAMMER

PNAME (VARCHAR), DOB (DATE), DOJ (DATE), SEX (CHAR), PROF1 (VARCHAR), PROF2 (VARCHAR), SAL (NUMBER)

LEGEND :

PNAME – Programmer Name, SPLACE – Study Place, CCOST – Course Cost,  DEVIN – Developed in, SCOST – Software Cost, DCOST – Development Cost, PROF1 – Proficiency 1

QUERIES :

1. Find out the selling cost average for packages developed in Oracle.
2. Display the names, ages and experience of all programmers.
3. Display the names of those who have done the PGDCA course.
4. What is the highest number of copies sold by a package?
5. Display the names and date of birth of all programmers born in April.
6. Display the lowest course fee.
7. How many programmers have done the DCA course.
8. How much revenue has been earned through the sale of packages developed in C.
9. Display the details of software developed by Rakesh.
10. How many programmers studied at Pentafour.
11. Display the details of packages whose sales crossed the 5000 mark.
12. Find out the number of copies which should be sold in order to recover the development cost of each package.
13. Display the details of packages for which the development cost has been recovered.
14. What is the price of costliest software developed in VB?
15. How many packages were developed in Oracle ?
16. How many programmers studied at PRAGATHI?
17. How many programmers paid 10000 to 15000 for the course?
18. What is the average course fee?
19. Display the details of programmers knowing C.
20. How many programmers know either C or Pascal?
21. How many programmers don’t know C and C++?
22. How old is the oldest male programmer?
23. What is the average age of female programmers?
24. Calculate the experience in years for each programmer and display along with their names in descending order.
25. Who are the programmers who celebrate their birthdays during the current month?
26. How many female programmers are there?
27. What are the languages known by the male programmers?
28. What is the average salary?
29. How many people draw 5000 to 7500?
30. Display the details of those who don’t know C, C++ or Pascal.
31. Display the costliest package developed by each programmer.
32. Produce the following output for all the male programmers

Programmer

      Mr. Arvind – has 15 years of experience

KEYS:

1. SELECT AVG(SCOST)  FROM SOFTWARE WHERE DEVIN = 'ORACLE';
2. SELECT PNAME,TRUNC(MONTHS_BETWEEN(SYSDATE,DOB)/12) "AGE", TRUNC(MONTHS_BETWEEN(SYSDATE,DOJ)/12) "EXPERIENCE" FROM PROGRAMMER;
3. SELECT PNAME FROM STUDIES WHERE COURSE = 'PGDCA';
4. SELECT MAX(SOLD) FROM SOFTWARE;
5. SELECT PNAME, DOB FROM PROGRAMMER WHERE DOB LIKE '%APR%';
6. SELECT MIN(CCOST) FROM STUDIES;
7. SELECT COUNT(*) FROM STUDIES WHERE COURSE = 'DCA';
8. SELECT SUM(SCOST*SOLD-DCOST) FROM SOFTWARE GROUP BY DEVIN HAVING DEVIN = 'C';
9. SELECT * FROM SOFTWARE WHERE PNAME = 'RAKESH';
10. SELECT * FROM STUDIES WHERE SPLACE = 'PENTAFOUR';
11. SELECT * FROM SOFTWARE WHERE SCOST*SOLD-DCOST > 5000;
12. SELECT CEIL(DCOST/SCOST) FROM SOFTWARE;
13. SELECT * FROM SOFTWARE WHERE SCOST*SOLD >= DCOST;
14. SELECT MAX(SCOST) FROM SOFTWARE GROUP BY DEVIN HAVING DEVIN = 'VB';
15. SELECT COUNT(*) FROM SOFTWARE WHERE DEVIN = 'ORACLE';
16. SELECT COUNT(*) FROM STUDIES WHERE SPLACE = 'PRAGATHI';
17. SELECT COUNT(*) FROM STUDIES WHERE CCOST BETWEEN 10000 AND 15000;
18. SELECT AVG(CCOST) FROM STUDIES;
19. SELECT * FROM PROGRAMMER WHERE PROF1 = 'C' OR PROF2 = 'C';
20. SELECT * FROM PROGRAMMER WHERE PROF1 IN ('C','PASCAL') OR PROF2 IN ('C','PASCAL');
21. SELECT * FROM PROGRAMMER WHERE PROF1 NOT IN ('C','C++') AND PROF2 NOT IN ('C','C++');
22. SELECT TRUNC(MAX(MONTHS_BETWEEN(SYSDATE,DOB)/12)) FROM PROGRAMMER WHERE S6/27/2006EX = 'M';
23. SELECT TRUNC(AVG(MONTHS_BETWEEN(SYSDATE,DOB)/12)) FROM PROGRAMMER WHERE SEX = 'F';
24. SELECT PNAME, TRUNC(MONTHS_BETWEEN(SYSDATE,DOJ)/12) FROM PROGRAMMER ORDER BY PNAME DESC;
25. SELECT PNAME FROM PROGRAMMER WHERE TO_CHAR(DOB,'MON') = TO_CHAR(SYSDATE,'MON');
26. SELECT COUNT(*) FROM PROGRAMMER WHERE SEX = 'F';
27. SELECT DISTINCT(PROF1) FROM PROGRAMMER WHERE SEX = 'M';
28. SELECT AVG(SAL) FROM PROGRAMMER;
29. SELECT COUNT(*) FROM PROGRAMMER WHERE SAL BETWEEN 5000 AND 7500;
30. SELECT * FROM PROGRAMMER WHERE PROF1 NOT IN ('C','C++','PASCAL') AND PROF2 NOT IN ('C','C++','PASCAL');6/27/2006
31. SELECT PNAME,TITLE,SCOST FROM SOFTWARE WHERE SCOST IN (SELECT MAX(SCOST) FROM SOFTWARE GROUP BY PNAME);

32.SELECT 'Mr.' || PNAME || ' - has ' || TRUNC(MONTHS_BETWEEN(SYSDATE,DOJ)/12) || ' years of experience' “Programmer” FROM PROGRAMMER WHERE SEX = 'M' UNION SELECT 'Ms.' || PNAME || ' - has ' || TRUNC (MONTHS_BETWEEN (SYSDATE,DOJ)/12)  || ' years of experience' “Programmer” FROM PROGRAMMER WHERE SEX = 'F';

II . SCHEMA :

Table 1 : DEPT

DEPTNO (NOT NULL , NUMBER(2)),  DNAME (VARCHAR2(14)),

LOC (VARCHAR2(13)

Table 2 : EMP

EMPNO (NOT NULL , NUMBER(4)), ENAME (VARCHAR2(10)),

JOB (VARCHAR2(9)), MGR (NUMBER(4)), HIREDATE (DATE),

SAL (NUMBER(7,2)), COMM (NUMBER(7,2)), DEPTNO (NUMBER(2))

MGR is the empno of the employee whom the employee reports to. DEPTNO is a foreign key.

QUERIES

1.      List all the employees who have at least one person reporting to them.

2.      List the employee details if and only if more than 10 employees are present in department no 10.

3.      List the name of the employees with their immediate higher authority.

4.      List all the employees who do not manage any one.

5.      List the employee details whose salary is greater than the lowest salary of an employee belonging to deptno 20.

6.      List the details of the employee earning more than the highest paid manager.

7.      List the highest salary paid for each job.

8.      Find the most recently hired employee in each department.

9.      In which year did most people join the company? Display the year and the number of employees.

10.  Which department has the highest annual remuneration bill?

11.  Write a query to display a ‘*’ against the row of the most recently hired employee.

12.  Write a correlated sub-query to list out the employees who earn more than the average salary of their department.

13.  Find the nth maximum salary.

14.  Select the duplicate records (Records, which are inserted, that already exist) in the EMP table.

15.  Write a query to list the length of service of the employees (of the form n years and m months).

KEYS:

1.      SELECT DISTINCT(A.ENAME) FROM EMP A, EMP B WHERE A.EMPNO = B.MGR;   or  SELECT ENAME FROM EMP WHERE EMPNO IN (SELECT MGR FROM EMP);

2.      SELECT * FROM EMP WHERE DEPTNO IN (SELECT DEPTNO FROM EMP GROUP BY DEPTNO HAVING COUNT(EMPNO)>10 AND DEPTNO=10);

3.      SELECT A.ENAME "EMPLOYEE", B.ENAME "REPORTS TO" FROM EMP A, EMP B WHERE A.MGR=B.EMPNO;

4.      SELECT * FROM EMP WHERE EMPNO IN ( SELECT EMPNO FROM EMP MINUS SELECT MGR FROM EMP);

5.      SELECT * FROM EMP WHERE SAL > ( SELECT MIN(SAL) FROM EMP GROUP BY DEPTNO HAVING DEPTNO=20);

6.      SELECT * FROM EMP WHERE SAL > ( SELECT MAX(SAL) FROM EMP GROUP BY JOB HAVING JOB = 'MANAGER' );

7.      SELECT JOB, MAX(SAL) FROM EMP GROUP BY JOB;

8.      SELECT * FROM EMP WHERE (DEPTNO, HIREDATE) IN (SELECT DEPTNO, MAX(HIREDATE) FROM EMP GROUP BY DEPTNO);

9.      SELECT TO_CHAR(HIREDATE,'YYYY') "YEAR", COUNT(EMPNO) "NO. OF EMPLOYEES" FROM EMP GROUP BY TO_CHAR(HIREDATE,'YYYY') HAVING COUNT(EMPNO) = (SELECT MAX(COUNT(EMPNO)) FROM EMP GROUP BY TO_CHAR(HIREDATE,'YYYY'));

10.  SELECT DEPTNO, LPAD(SUM(12*(SAL+NVL(COMM,0))),15) "COMPENSATION" FROM EMP GROUP BY DEPTNO HAVING SUM( 12*(SAL+NVL(COMM,0))) = (SELECT MAX(SUM(12*(SAL+NVL(COMM,0)))) FROM EMP GROUP BY DEPTNO);

11.  SELECT ENAME, HIREDATE, LPAD('*',8) "RECENTLY HIRED" FROM EMP WHERE HIREDATE = (SELECT MAX(HIREDATE) FROM EMP) UNION SELECT ENAME NAME, HIREDATE, LPAD(' ',15) "RECENTLY HIRED" FROM EMP WHERE HIREDATE != (SELECT MAX(HIREDATE) FROM EMP);

12.  SELECT ENAME,SAL FROM EMP E WHERE SAL > (SELECT AVG(SAL) FROM EMP F WHERE E.DEPTNO = F.DEPTNO);

13.  SELECT ENAME, SAL FROM EMP A WHERE &N = (SELECT COUNT (DISTINCT(SAL)) FROM EMP B WHERE A.SAL<=B.SAL);

14.  SELECT * FROM EMP A WHERE A.EMPNO IN (SELECT EMPNO FROM EMP GROUP BY EMPNO HAVING COUNT(EMPNO)>1) AND A.ROWID!=MIN (ROWID));

15.  SELECT ENAME "EMPLOYEE",TO_CHAR(TRUNC(MONTHS_BETWEEN(SYSDATE,HIREDATE)/12))||' YEARS '|| TO_CHAR(TRUNC(MOD(MONTHS_BETWEEN (SYSDATE, HIREDATE),12)))||' MONTHS ' "LENGTH OF SERVICE" FROM EMP;