DBMS [ 6 ]

501. What are the cursor attributes used in PL/SQL ?

%ISOPEN - to check whether cursor is open or not
% ROWCOUNT - number of rows fetched/updated/deleted.
% FOUND - to check whether cursor has fetched any row. True if rows
are fetched.
% NOT FOUND - to check whether cursor has fetched any row. True if
no rows are featched.
These attributes are proceeded with SQL for Implicit Cursors and
with Cursor name for Explicit Cursors.

502. What are % TYPE and % ROWTYPE ? What are the advantages of
using these over datatypes?

% TYPE provides the data type of a variable or a database column to
that variable.
% ROWTYPE provides the record type that represents a entire row of a
table or view or columns selected in the cursor.
The advantages are :
I. Need not know about variable's data type
ii. If the database definition of a column in a table changes, the
data type of a variable changes accordingly.

503. What is difference between % ROWTYPE and TYPE RECORD ?

% ROWTYPE is to be used whenever query returns a entire row of a
table or view.
TYPE rec RECORD is to be used whenever query returns columns of
different table or views and variables.
E.g. TYPE r_emp is RECORD (eno emp.empno% type,ename emp ename %
type );
e_rec emp% ROWTYPE
cursor c1 is select empno,deptno from emp;
e_rec c1 %ROWTYPE.

504. What are the different types of PL/SQL program units that can
be defined and stored in ORACLE database ?

Procedures and Functions,Packages and Database Triggers.

505. What are the advantages of having a Package ?

Increased functionality (for example,global package variables can be
declared and used by any proecdure in the package) and performance
(for example all objects of the package are parsed compiled, and
loaded into memory once)

506. What are the uses of Database Trigger ?

Database triggers can be used to automatic data generation, audit
data modifications, enforce complex Integrity constraints, and
customize complex security authorizations.

507. What is a Procedure ?

A Procedure consist of a set of SQL and PL/SQL statements that are
grouped together as a unit to solve a specific problem or perform a
set of related tasks.

508. What is a Package ?

A Package is a collection of related procedures, functions,
variables and other package constructs together as a unit in the
database.

509. What is difference between Procedures and Functions ?

A Function returns a value to the caller where as a Procedure does
not.

510. What is Database Trigger ?

A Database Trigger is procedure (set of SQL and PL/SQL statements)
that is automatically executed as a result of an insert in,update
to, or delete from a table.

511. Can the default values be assigned to actual parameters?

Yes

512. Can a primary key contain more than one columns?

Yes

513. 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.

514. 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.

515. Differentiate 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 ROLLBACK
One can Rollback
Doesn't have selective features (where clause)
Has
Doesn't fire database triggers
Does
It requires disabling of referential constraints.

516. 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

517. 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

518. What are different Oracle database objects?

-TABLES
-VIEWS
-INDEXES
-SYNONYMS
-SEQUENCES
-TABLESPACES etc

519. 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 '-')

520. 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.

521. 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.

522. 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.

523. 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.

524. What are various privileges that a user can grant to another
user?

-SELECT
-CONNECT
-RESOURCES

525. 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);

526. 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

527. 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.

528. Difference between an implicit & an explicit cursor.?

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.

529. 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.

530. 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.

531. 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.

532. 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

533. 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.

534. 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


535. What are various constraints used in SQL?

-NULL
-NOT NULL
-CHECK
-DEFAULT

536. 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.

537. 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.

538. Can you use a commit statement within a database trigger?

No

539. 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
FHKO;;;;;;;;;SET current_credits=current_credits+v_numcredits
WHERE CURRENT OF X;

540. 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

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

-IN -OUT -INOUT

542. 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.

543. When do you use WHERE clause and when do 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.

544. 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.

545. Which is more faster - IN or EXISTS?

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

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

Drop Procedure procedure_name
Drop Function function_name

547. 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);

548. Difference between database triggers and form triggers?

-Data base trigger(DBT) fires when a DML opperation is performed on
a data base table. Form trigger(FT) Fires when user presses a key or
navigates between fields on the screen
-Can be row level or statement level No disstinction between row
level and statement level.
-Can manipulate data stored in Oracle tablees via SQL Can manipulate
data in Oracle tables as well as variables in forms.
-Can be fired from any session executing thhe triggering DML
statements. Can be fired only from the form that define the trigger.
-Can cause other database triggers to fire..Can cause other database
triggers to fire, but not other form triggers.

549. 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.

550. How you will avoid duplicating records in a query?

By using DISTINCT

551. What is a view ?

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

552. 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.

553. 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.

554. 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.

555. What is the maximum buffer size that can be specified using the
DBMS_OUTPUT.ENABLE function?

1,000,00

556. What are cursor attributes?

-%ROWCOUNT
-%NOTFOUND
-%FOUND
-%ISOPEN

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

'' Should be used before '%'.

558. What is ON DELETE CASCADE ?

When ON DELETE CASCADE is specified ORACLE maintains referential
integrity by automatically removing dependent foreign key values if
a referenced primary or unique key value is removed.

559. What is the fastest way of accessing a row in a table ?

Using ROWID.CONSTRAINTS

560. What is difference between TRUNCATE & DELETE ?

TRUNCATE commits after deleting entire table i.e., can not be rolled
back. Database triggers do not fire on TRUNCATEDELETE allows the
filtered deletion. Deleted records can be rolled back or
committed.Database triggers fire on DELETE.

561. What is a transaction ?

Transaction is logical unit between two commits and commit and
rollback.

562. What are the advantages of VIEW ?

To protect some of the columns of a table from other users.To hide
complexity of a query.To hide complexity of calculations.

563. How will you a activate/deactivate integrity constraints ?

The integrity constraints can be enabled or disabled by ALTER TABLE
ENABLE constraint/DISABLE constraint.

564. Where the integrity constraints are stored in Data Dictionary ?

The integrity constraints are stored in USER_CONSTRAINTS.

565. What is the Subquery ?

Sub query is a query whose return values are used in filtering
conditions of the main query.

566. How to access the current value and next value from a
sequence ? Is it possible to access the current value in a session
before accessing next value ?

Sequence name CURRVAL, Sequence name NEXTVAL.It is not possible.
Only if you access next value in the session, current value can be
accessed.

567. What are the usage of SAVEPOINTS ?value in a session before
accessing next value ?

SAVEPOINTS are used to subdivide a transaction into smaller parts.
It enables rolling back part of a transaction. Maximum of five save
points are allowed.

568. What is ROWID ?in a session before accessing next value ?

ROWID is a pseudo column attached to each row of a table. It is 18
character long, blockno, rownumber are the components of ROWID.

569. Explain Connect by Prior ?in a session before accessing next
value ?

Retrieves rows in hierarchical order.e.g. select empno, ename from
emp where.

570. How many LONG columns are allowed in a table ? Is it possible
to use LONG columns in WHERE clause or ORDER BY ?

Only one LONG columns is allowed. It is not possible to use LONG
column in WHERE or ORDER BY clause.

571. What is Referential Integrity ?

Maintaining data integrity through a set of rules that restrict the
values of one or more columns of the tables based on the values of
primary key or unique key of the referenced table.

572. What is a join ? Explain the different types of joins ?

Join is a query which retrieves related columns or rows from
multiple tables.Self Join - Joining the table with itself.Equi Join -
Joining two tables by equating two common columns.Non-Equi Join -
Joining two tables by equating two common columns.Outer Join -
Joining two tables in such a way that query can also retrieve rows
that do not have corresponding join value in the other table.

573. If an unique key constraint on DATE column is created, will it
validate the rows that are inserted with SYSDATE ?

It won't, Because SYSDATE format contains time attached with it.

574. Explain UNION,MINUS,UNION ALL, INTERSECT ?

INTERSECT returns all distinct rows selected by both queries.MINUS -
returns all distinct rows selected by the first query but not by the
second.UNION - returns all distinct rows selected by either
queryUNION ALL - returns all rows selected by either query,
including all duplicates.

575. What is an Integrity Constraint ?

Integrity constraint is a rule that restricts values to a column in
a table.

576. Difference between SUBSTR and INSTR ?

INSTR (String1,String2(n,(m)),INSTR returns the position of the mth
occurrence of the string 2 instring1. The search begins from nth
position of string1.SUBSTR (String1 n,m)SUBSTR returns a character
string of size m in string1, starting from nth position of string1.

577. If a View on a single base table is manipulated will the
changes be reflected on the base table ?

If changes are made to the tables which are base tables of a view
will the changes be reference on the view.

578. What are the pre requisites ?

I. to modify data type of a column ? ii. to add a column with NOT
NULL constraint ? To Modify the datatype of a column the column must
be empty. to add a column with NOT NULL constrain, the table must be
empty.

579. What is a database link ?

Database Link is a named path through which a remote database can be
accessed.

580. What are the types of SQL Statement ?

Data Definition Language :
CREATE,ALTER,DROP,TRUNCATE,REVOKE,NO AUDIT & COMMIT.

Data Manipulation Language:
INSERT,UPDATE,DELETE,LOCK

TABLE,EXPLAIN PLAN & SELECT.Transactional Control:
COMMIT & ROLLBACKSession Control: ALTERSESSION & SET

ROLESystem Control :
ALTER SYSTEM.

581. What is CYCLE/NO CYCLE in a Sequence ?

CYCLE specifies that the sequence continues to generate values after
reaching either maximum or minimum value. After pan ascending
sequence reaches its maximum value, it generates its minimum value.
After a descending sequence reaches its minimum, it generates its
maximum.NO CYCLE specifies that the sequence cannot generate more
values after reaching its maximum or minimum value.

582. What is correlated sub-query ?

Correlated sub query is a sub query which has reference to the main
query.

583. What are the data types allowed in a table ?

CHAR,VARCHAR2,NUMBER,DATE,RAW,LONG and LONG RAW.

584. What is difference between CHAR and VARCHAR2 ? What is the
maximum SIZE allowed for each type ?

CHAR pads blank spaces to the maximum length. VARCHAR2 does not pad
blank spaces. For CHAR it is 255 and 2000 for VARCHAR2.

585. Can a view be updated/inserted/deleted? If Yes under what
conditions ?

A View can be updated/deleted/inserted if it has only one base table
if the view is based on columns from one or more tables then insert,
update and delete is not possible.

586. What are the different types of Coordinations of the Master
with the Detail block?

POPULATE_GROUP(function)
POPULATE_GROUP_WITH_QUERY(function)
SET_GROUP_CHAR_CELL(procedure)
SET_GROUPCELL(procedure)
SET_GROUP_NUMBER_CELL(procedure)

587. Use the ADD_GROUP_COLUMN function to add a column to a record
group that was created at design time? I) TRUE II)FALSE

II) FALSE

588. Use the ADD_GROUP_ROW procedure to add a row to a static record
group? I) TRUE II)FALSE

I) FALSE

589. 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

590. 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

591. Suppose a customer table is 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)

592. 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