Sql Question And Answers

Sql Question and answer 8

2008-01-18T16:35:00.002+05:30

31. What are ORACLE PRECOMPILERS.

Using ORACLE PRECOMPILERS ,SQL statements and PL/SQL blocks can be contained
inside 3GL programs written in C,C++,COBOL,PASCAL, FORTRAN,PL/1 AND ADA.

The Precompilers are known as Pro*C,Pro*Cobol,...
This form of PL/SQL is known as embedded pl/sql,the language in which pl/sql is
embedded is known as the host language.

The prcompiler translates the embedded SQL and pl/sql ststements into calls to the
precompiler runtime library.The output must be compiled and linked with this library to
creater an executable.

32. What is OCI. What are its uses.

Oracle Call Interface is a method of accesing database
from a 3GL program. Uses--No precompiler is required,PL/SQL blocks are executed like
other DML
statements.
The OCI library provides
-functions to parse SQL statemets
-bind input variables
-bind output variables
-execute statements
-fetch the results

33. Difference between database triggers and form triggers.

a) Data base trigger(DBT) fires when a DML operation is performed on a data base table.Form trigger(FT) Fires when user presses a key or navigates between fields on the screen

b) Can be row level or statement level No distinction between row level and statement level.

c) Can manipulate data stored in Oracle tables via SQL Can manipulate data in Oracle tables as well as
variables in forms.

d) Can be fired from any session executing the triggering DML statements. Can be fired only from the form that define the trigger.

e) Can cause other database triggers to fire.Can cause other database triggers to fire,but not other form triggers.

34. What is an UTL_FILE.What are different procedures and functions associated with it.

UTL_FILE is a package that adds the ability to read and write to operating system files
Procedures associated with it are FCLOSE, FCLOSE_ALL and 5 procedures to output
data to a file PUT, PUT_LINE, NEW_LINE, PUTF, FFLUSH.PUT, FFLUSH.PUT_LINE,FFLUSH.NEW_LINE. Functions associated with it are FOPEN, ISOPEN.

35. Can you use a commit statement within a database trigger.
No

36. What is the maximum buffer size that can be specified using the DBMS_OUTPUT.ENABLE function?
1,000,000

Sql Question and answer 7

2008-01-18T16:35:00.001+05:30

31. How you were passing cursor variables in PL/SQL 2.2.
In PL/SQL 2.2 cursor variables cannot be declared in a package.This is because the storage for a cursor variable has to be allocated using Pro*C or OCI with version 2.2,the only means of passing a cursor variable to a PL/SQL block is via bind variable or a procedure parameter.

32. Can cursor variables be stored in PL/SQL tables.If yes how.If not why.

No, a cursor variable points a row which cannot be stored in a two-dimensional PL/SQL table.

33. Difference between procedure and function.

Functions are named PL/SQL blocks that return a value and can be called with arguments procedure a named block that can be called with parameter. A procedure all is a PL/SQL statement by itself, while a Function call is called as part of an expression.

34. What are different modes of parameters used in functions and procedures.

IN
OUT
INOUT

35. What is difference between a formal and an actual parameter

The variables declared in the procedure and which are passed, as arguments are called
actual, the parameters in the procedure declaration. Actual parameters contain the
values that are passed to a procedure and receive results. Formal parameters are the
placeholders for the values of actual parameters

36. Can the default values be assigned to actual parameters.

Yes

37. Can a function take OUT parameters.If not why.

No.A function has to return a value,an OUT parameter cannot return a value.

38. What is syntax for dropping a procedure and a function .Are these operations possible.

Drop Procedure procedure_name
Drop Function function_name

Sql Question and answer 6

2008-01-18T16:34:00.001+05:30

31. What a SELECT FOR UPDATE cursor represent.

SELECT......FROM......FOR......UPDATE[OF column-reference][NOWAIT] The
processing done in a fetch loop modifies the rows that have been retrieved by the
cursor.

A convenient way of modifying the rows is done by a method with two parts: the FOR
UPDATE clause in the cursor declaration, WHERE CURRENT OF CLAUSE in an
UPDATE or declaration statement.

32. What 'WHERE CURRENT OF ' clause does in a cursor.

LOOP
SELECT num_credits INTO v_numcredits FROM classes
WHERE dept=123 and course=101;
UPDATE students
SET current_credits=current_credits+v_numcredits
WHERE CURRENT OF X;
END LOOP
COMMIT;
END;

33. What is use of a cursor variable? How it is defined.

A cursor variable is associated with different statements at run time, which can hold
different values at run time. Static cursors can only be associated with one run time
query. A cursor variable is reference type(like a pointer in C).

Declaring a cursor variable:
TYPE type_name IS REF CURSOR RETURN return_type type_name is the name of
the reference type,return_type is a record type indicating the types of the select list
that will eventually be returned by the cursor variable.

34. What should be the return type for a cursor variable.Can we use a scalar data type as return type.
The return type for a cursor must be a record type.It can be declared explicitly as a
user-defined or %ROWTYPE can be used. eg TYPE t_studentsref IS REF
CURSOR RETURN students%ROWTYPE

35. How you open and close a cursor variable.Why it is required.

OPEN cursor variable FOR SELECT...Statement
CLOSE cursor variable In order to associate a cursor variable with a particular
SELECT statement OPEN syntax is used.In order to free the resources used
for the query CLOSE
statement is used.

Sql Question and answer 5

2008-01-18T16:33:00.001+05:30

PL-SQL QUESTIONS

If you know pl-sql read it further otherwise better stop with sql alone and move to java at the bottom of the page (if you are a java guy), that should be sufficient.

1. What is the purpose of a cluster.

Oracle does not allow a user to specifically locate tables, since that is a part of the
function of the RDBMS. However, for the purpose of increasing performance, oracle allows a developer to create a CLUSTER. A CLUSTER provides a means for storing
data from different tables together for faster retrieval than if the table placement were
left to the RDBMS.

2. What is a cursor.

Oracle uses work area to execute SQL statements and store processing information
PL/SQL construct called a cursor lets you name a work area and access its stored
information A cursor is a mechanism used to fetch more than one row in a Pl/SQl
block.

3. Difference between an implicit & an explicit cursor.

PL/SQL declares a cursor implicitly for all SQL data manipulation statements, including
quries that return only one row. However,queries that return more than one row you
must declare an explicit cursor or use a cursor FOR loop.

Explicit cursor is a cursor in which the cursor name is explicitly assigned to a SELECT
statement via the CURSOR...IS statement. An implicit cursor is used for all SQL statements Declare, Open, Fetch, Close. An explicit cursors are used to process multirow SELECT statements An implicit cursor is used to process INSERT, UPDATE,
DELETE and single row SELECT. .INTO statements.

4. What are cursor attributes

%ROWCOUNT
%NOTFOUND
%FOUND
%ISOPEN

5. What is a cursor for loop.

Cursor For Loop is a loop where oracle implicitly declares a loop variable, the loop index that of the same record type as the cursor's record.

6. Difference between NO DATA FOUND and %NOTFOUND

NO DATA FOUND is an exception raised only for the SELECT....INTO statements
when the where clause of the querydoes not match any rows. When the where clause
of the explicit cursor does not match any rows the %NOTFOUND attribute is set to
TRUE instead.

Sql Question and answer

2008-01-18T16:32:00.000+05:30

1. Suppose customer table is there having different columns
like customer no, payments.What will be the query to select top three max payments.

SELECT customer_no, payments from customer C1
WHERE 3<=(SELECT COUNT(*) from customer C2
WHERE C1.payment <= C2.payment)

Display the records between two range

select rownum, empno, ename from emp where rowid in
(select rowid from emp where rownum <=&upto
minus select rowid from emp where rownum<&Start);

Find out nth highest salary from emp table
SELECT DISTINCT (a.sal) FROM EMP A WHERE &N = (SELECT COUNT (DISTINCT (b.sal)) FROM EMP B WHERE a.sal<=b.sal);
For Eg:-
Enter value for n: 2
SAL
---------
3700

Display the number value in Words
SQL> select sal, (to_char(to_date(sal,'j'), 'jsp'))
from emp;

the output like,
SAL (TO_CHAR(TO_DATE(SAL,'J'),'JSP'))
--------- -----------------------------------------------------
800 eight hundred
1600 one thousand six hundred
1250 one thousand two hundred fifty
If you want to add some text like,
Rs. Three Thousand only.
SQL> select sal "Salary ",
(' Rs. '|| (to_char(to_date(sal,'j'), 'Jsp'))|| ' only.'))
"Sal in Words" from emp
/
Salary Sal in Words
------- ------------------------------------------------------
800 Rs. Eight Hundred only.
1600 Rs. One Thousand Six Hundred only.
1250 Rs. One Thousand Two Hundred Fifty only.

14. Display Odd/ Even number of records
Odd number of records:
select * from emp where (rowid,1) in (select rowid, mod(rownum,2) from emp);
Output:-
1
3
5

Even number of records:
select * from emp where (rowid,0) in (select rowid, mod(rownum,2) from emp)
Output:-

2
4
6

'How do you find the numbert of rows in a Table ?'
A bad answer is count them (SELECT COUNT(*) FROM table_name)

A good answer is :-
'By generating SQL to ANALYZE TABLE table_name COUNT STATISTICS by querying Oracle System Catalogues (e.g. USER_TABLES or ALL_TABLES).

The best answer is to refer to the utility which Oracle released which makes it
unnecessary to do ANALYZE TABLE for each Table individually.

minvalue.sql
Select the Nth lowest value from a table

select level, min('col_name') from my_table where level = '&n' connect by prior ('col_name') < 'col_name')
group by level;

Example:

Given a table called emp with the following columns:
-- id number
-- name varchar2(20)
-- sal number
--
-- For the second lowest salary:

-- select level, min(sal) from emp
-- where level=2
-- connect by prior sal < sal
-- group by level

maxvalue.sql
Select the Nth Highest value from a table

select level, max('col_name') from my_table where level = '&n' connect by prior ('col_name') > 'col_name')
group by level;

Example:

Given a table called emp with the following columns:
-- id number
-- name varchar2(20)
-- sal number
--
-- For the second highest salary:

-- select level, max(sal) from emp
-- where level=2
-- connect by prior sal > sal
-- group by level

Sql Question and answer 4

2008-01-18T16:31:00.000+05:30

1. When you use WHERE clause and when you use HAVING clause

HAVING clause is used when you want to specify a condition for a group function and it
is written after GROUP BY clause

The WHERE clause is used when you want to specify a condition for columns, single
row functions except group functions and it is written before GROUP BY clause if it is
used.

2. Which is more faster - IN or EXISTS

EXISTS is more faster than IN because EXISTS returns
a Boolean value whereas IN returns a value.

3. What is a OUTER JOIN

Outer Join--Its a join condition used where you can query all the rows of one of the
tables in the join condition even though they don’t satisfy the join condition.

4. How you will avoid your query from using indexes

SELECT * FROM emp
Where emp_no+' '=12345;

i.e you have to concatenate the column name with
space within codes in the where condition.

SELECT /*+ FULL(a) */ ename, emp_no from emp
where emp_no=1234;
i.e using HINTS

5. What is a pseudo column. Give some examples

It is a column that is not an actual column in the
table.

eg USER, UID, SYSDATE, ROWNUM, ROWID, NULL, AND LEVEL

Sql Question and answer 3

2008-01-18T16:29:00.000+05:30

1. What is difference between SQL and SQL*PLUS

SQL*PLUS is a command line tool where as SQL and PL/SQL language interface and
reporting tool. Its a command line tool that allows user to type SQL commands to be
executed directly against an Oracle database. SQL is a language used to query the
relational database(DML,DCL,DDL). SQL*PLUS commands are used to format query
result, Set options, Edit SQL commands and PL/SQL.

2. Which datatype is used for storing graphics and images

LONG RAW data type is used for storing BLOB's (binary large objects).

3. How will you delete duplicating rows from a base table
delete from table_name where rowid not in (select max(rowid) from table group by duplicate_values_field_name);

or

delete duplicate_values_field_name dv from table_name ta where rowid <(select min(rowid) from table_name tb where ta.dv=tb.dv);

4. What is difference between SUBSTR and INSTR

SUBSTR returns a specified portion of a string
eg SUBSTR('BCDEF',4) output BCDE
INSTR provides character position in which a pattern
is found in a string.

eg INSTR('ABC-DC-F','-',2) output 7 (2nd occurence of '-')

5. There is a string '120000 12 0 .125' ,how you will find the
position of the decimal place

INSTR('120000 12 0 .125',1,'.')
output 13

6. There is a '%' sign in one field of a column. What will be
the query to find it.

'\' Should be used before '%'.

Sql Question and answer 2

2008-01-18T16:28:00.000+05:30

1. What are different Oracle database objects

TABLES
VIEWS
INDEXES
SYNONYMS
SEQUENCES
TABLESPACES etc

2. What is difference between Rename and Alias

Rename is a permanent name given to a table or column whereas Alias is a temporary
name given to a table or column which do not exist once the SQL statement is
executed.

3. What is a view

A view is stored procedure based on one or more tables, it’s a virtual table.

What are various privileges that a user can grant to another user

SELECT
CONNECT
RESOURCES

4. What is difference between UNIQUE and PRIMARY KEY constraints

A table can have only one PRIMARY KEY whereas there can be any number of UNIQUE keys.
The columns that compose PK are automatically define NOT NULL, whereas a column that compose a UNIQUE is not automatically defined to be mandatory must also specify the column is NOT NULL.

5. Can a primary key contain more than one columns

Yes

6. How you will avoid duplicating records in a query

By using DISTINCT

Sql Question and answer 1

2008-01-18T16:26:00.001+05:30

1. Difference between group functions and single row functions.

Group Function Single Row Function
A group function operates A single row function
on many rows returns one and result for one row.
returns single result.

Not allowed in Pl/sql procedural Allowed in Pl/Sql
Procedural statements
statements.
eg SUM(),AVG,MIN,MAX etc eg UPPER,LOWER,CHR...

2. Difference between DECODE and TRANSLATE

DECODE is value by value TRANSLATE is character by
character replacement. replacement.
Ex SELECT DECODE('ABC','A',1,'B',2,'ABC',3) eg SELECT
from dual; o/p 3 TRANSLATE('ABCGH',
'ABCDEFGHIJ', 1234567899)
FROM DUAL; o/p 12378

(DECODE command is used to bring IF,THEN,ELSE logic to SQL.It tests for the IF values(s) and then aplies THEN value(s) when true, the ELSE value(s) if not.)

3. Difference between TRUNCATE and DELETE

TRUNCATE deletes much faster than DELETE

Truncate Delete
It is a DDL statement It is a DML statement
It is a one way trip,cannot One can Rollback
ROLLBACK
Doesn't have selective features (where clause) Has
Doesn't fire database triggers Does
It requires disabling of referential Does not require
constraints.

4. What is a CO-RELATED SUBQUERY

A CO-RELATED SUBQUERY is one that has a correlation
name as table or view designator in the FROM clause of the outer
query and the same correlation name as a qualifier of a search
condition in the WHERE clause of the subquery.

eg
SELECT field1 from table1 X
WHERE field2>(select avg(field2) from table1 Y
where
field1=X.field1);

(The subquery in a correlated subquery is revaluated
for every row of the table or view named in the outer query.)

5. What are various joins used while writing SUBQUERIES

Self join-Its a join foreign key of a table references the same table.

Outer Join--Its a join condition used where One can query all the rows of one of the
tables in the join condition even though they don't satisfy the join condition.

Equi-join--Its a join condition that retrieves rows from one or more tables in which one
or more columns in one table are equal to one or more columns in the second table.

6. What are various constraints used in SQL

NULL
NOT NULL
CHECK
DEFAULT

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2008-01-18T16:23:00.001+05:30

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