Oracle PL-SQL Interview Preparation Guide

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Stored procedures are subprogrammes stored in the database and can be called &executee multiple times wherein an application procedure is the one being used for a particular application same is the way for function.

Both can be executed any number of times. Only difference is that stored procedures/ functions are stored in database in complied format while the application procedures/functions are not in precomplied format and at run time has to be compiled.

ROWID - Hexa decimal number each and every row having unique.Used in searching.

ROWNUM - It is a integer number also unique for sorting Normally TOP N Analysys.

Other Psudo Column are

NEXTVAL,CURRVAL Of sequence are some exampls

psudo columns are default columns provided by oracle

One must declare an identifier before referencing it. Once it is declared it can be referred even before defining it in the PL/SQL. This rule applies to function and procedures also.

s Distributed database system based on 2 phase commit,one query is independent of 2 nd query so of course we can run.

CREATE OR REPLACE PROCEDURE ddl_create_proc (p_table_name IN VARCHAR2)

AS

l_stmt VARCHAR2(200);

BEGIN

DBMS_OUTPUT.put_line('STARTING ');

l_stmt := 'create table '|| p_table_name || ' as (select * from emp )';

execute IMMEDIATE l_stmt;

DBMS_OUTPUT.put_line('end ');

EXCEPTION

WHEN OTHERS THEN

DBMS_OUTPUT.put_line('exception '||SQLERRM || 'message'||sqlcode);

END;

Just use subquery in for clause

ex:For emprec in (select * from emp)

loop

dbms_output.put_line(emprec.empno);

end loop;

no exit statement needed

implicit open,fetch,close occurs

Implicit Cursor are declared and used by the oracle internally. whereas the explicit cursors are declared and used by the user. more over implicitly cursors are no need to declare oracle creates and process and closes autometically. the explicit cursor should be declared and closed by the user.

Implicit cursors are used for single row query whereas explicit cursor is used for multiple row query

Execute procedure name (parameter1,parameter2)

Select timestamps, owner, obj_name, action_name from dba_audit_trail;this statement gives last executed time for procedure , function & package.

yes we can use objects, arrays to return more than one value

For improving performance, we need to check the sql statement blocks , because for every sql satement execution transfor to sql engine and come back to plsq engine that process takes more time to process the plsql block.

PL/SQL uses block structure as its basic structure. Anonymous blocks or nested blocks can be used in PL/SQL.

A set of related declarations and procedural statements is called block.

DECLARE -- declaration section BEGIN -- executable statements -- main section EXCEPTION -- handling possible exceptions -- occuring in the main section END;

Some scalar data types such as
NUMBER,
VARCHAR2,
DATE,
CHAR,
LONG,
BOOLEAN.
Some composite data types such as RECORD & TABLE.

% 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.

% 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.

One more point : When we have a variable of typer RECORD we have declare additional variables but with %rowtype, we can only have the fields that are present in the table

By declaring this cursor we can update the table emp through z,means wo not need to write table name for updation,it may be only by "z".

By issuing the TCL like commit or rollback, the cursor will be closed automatically, you cannat fetch again. You will get an error if yuo

Currently, cursor variables are subject to the following restrictions:You cannot declare cursor variables in a package spec. For example, the following declaration is not allowed:CREATE PACKAGE emp_stuff AS TYPE EmpCurTyp IS REF CURSOR RETURN emp%ROWTYPE; emp_cv EmpCurTyp; -- not allowedEND emp_stuff;You cannot pass cursor variables to a procedure that is called through a database link.If you pass a host cursor variable to PL/SQL, you cannot fetch from it on the server side unless you also open it there on the same server call.You cannot use comparison operators to test cursor variables for equality, inequality, or nullity.You cannot assign nulls to a cursor variable.Database columns cannot store the values of cursor variables. There is no equivalent type to use in a CREATE TABLE statement.You cannot store cursor variables in an associative array, nested table, or varray.Cursors and cursor variables are not interoperable; that is, you cannot use one where the other is expected. For example, you cannot reference a cursor variable in a cursor FOR loop

Yes,we can declare a column with above condition.table created successfully.

yes, 100 is the total size and 10 is included in 100

Cursor C1 is
Select empno,
ename from emp;
Begin
open C1; loop
Fetch C1 into
eno.ename;
Exit When
C1 %notfound;-----
commit;
end loop;
end;
The cursor having query as SELECT .... FOR UPDATE gets closed after COMMIT/ROLLBACK.
The cursor having query as SELECT.... does not get closed even after COMMIT/ROLLBACK.

WHERE CURRENT OF clause in an UPDATE,DELETE statement refers to the latest row fetched from a cursor. Database Triggers

Database trigger is stored PL/SQL program unit associated with a specific database table. Usages are Audit data modifications, Log events transparently, Enforce complex business rules Derive column values automatically, Implement complex security authorizations. Maintain replicate tables.

Insert Update Delete
Before Row o.k. o.k. o.k.
After Row o.k. o.k. o.k.
Before Statement o.k. o.k. o.k.
After Statement o.k. o.k. o.k.
If FOR EACH ROW clause is specified, then the trigger for each Row affected by the statement.
If WHEN clause is specified, the trigger fires according to the returned Boolean value.

It is not possible. As triggers are defined for each table, if you use COMMIT of ROLLBACK in a trigger, it affects logical transaction processing.

yes WE can use COMMIT and ROLLBACK triggers, but by using PRAGAMA AUTONAMOUS_TRANSATIONS. Now the transation treated as a autonomous tansation.

The table columns are referred as OLD.column_name and NEW.column_name.
For triggers related to INSERT only NEW.column_name values only available.
For triggers related to UPDATE only OLD.column_name NEW.column_name values only available.
For triggers related to DELETE only OLD.column_name values only available.

Mutation of table occurs.