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Cursors In Oracle

CURSOR : A cursors is a pointer used to fetch rows from a result set 
Two types of classification s:


I.STATIC CURSOR S: 
Static : Normal cursor (implicit or explicit)

Cursor attributes  for implicit and explicit:

%FOUND – records fetched successfully
%NOTFOUND – no records fetched
%ROWCOUNT – Number of records fetched
%ISOPEN – returns TRUE if cursor is open

a. Implicit : 
Cannot be opened outside the statement
More fast and less coding effort.
Will never raise INVALID_CURSOR error
Raises NO_DATA_FOUND and TOO_MANY_ROWS exceptions (eg: select <stmt>)

Example Implicit Cursor:

select * from emp

If SQL%FOUND then

v_count:= SQL%ROWCOUNT

end if;


b. Explicit : 2 network round trips. Store data first then retrieve data. 
More programmatic control.
Programmer could open; fetch data, close, check attributes etc.

Syntax:
open c1; — cursor c1 is select <stmt>

fetch <>

exit when c1%NOTFOUND

Example Explicit cursor:

Without Using Loop s
Declare

Cursor cur1 is

select ename,empno,sal from emp

where sal<50000 and deptno=50

begin

open cur1;

fetch cur1 into v_ename,v_empno,v_sal;

exit when cur1%notfound;

—<do processing>

close cur1;

end;

Using Loops:

Declare

Cursor cur1 is

select ename,empno,sal from emp

where sal<50000 and deptno=50

begin

For rec in cur1
loop
dbms_output.put_line(‘Employee Number ‘||rec.empno);
end loop;

end;

Using Loops with Cursor Parameters:

Declare

Cursor cur1( cp_deptNo Number) 
is
select ename,empno,sal from emp
where sal<50000 and deptno=cp_deptNo

l_deptNo Number :=50;
begin

For rec in cur1(l_deptNo)
loop
dbms_output.put_line(‘Employee Number ‘||rec.empno);
end loop;

end;

II. DYNAMIC CURSOR s : 

Oracle REF CURSOR Types:
With the REF_CURSOR you can return a recordset/cursor from a stored procedure
(i.e Ref Cursors can have Record/s as return types.)
Could be declared once and defined many times in different procedures. 

a)Strong : For the strong ref cursor the returning columns with data type and length need to be known at compile time.
b)Weak :For the weak ref cursor the structure does not need to be known at compile time.

Example For the Ref Cursor :


–SPECK PACKAGE 
CREATE OR REPLACE PACKAGE REFCURSOR_PKG
 AS
  TYPE WEAK_REF_CURSOR IS REF CURSOR; — Until 9i
  TYPE STRONG_REF_CURSOR IS REF CURSOR RETURN EMP%ROWTYPE;

END REFCURSOR_PKG;

The pl/sql procedure that returns a ref-cursor looks like this:


–BODY PACKAGE 
CREATE OR REPLACE PACKAGE BODY REFCURSOR_PKG
AS
— For Weak Ref Cursor: 
PROCEDURE 
WEAK_REF_CUR_PRC( p_deptno IN number,
                  p_cursor OUT REFCURSOR_PKG.WEAK_REF_CURSOR — Until 9i
                  —- From 9i (p_cursor OUT SYS_REFCURSOR )—-
                 )
IS

BEGIN

  OPEN p_cursor FOR
  SELECT *  FROM   emp
  WHERE  deptno = p_deptno;
end WEAK_REF_CUR_PRC;

— For Strong Ref Cursor: 
PROCEDURE 
STRONG_REF_CUR_PRC( p_deptno IN number,
                    p_cursor OUT REFCURSOR_PKG.STRONG_REF_CURSOR
                  )
IS

BEGIN
  SELECT *  FROM   emp
  WHERE  deptno = p_deptno;
  end STRONG_REF_CUR_PRC;
 END REFCURSOR_PKG;
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