CBSE Class 12 Informatics Practices Interacting With Databases Notes

CHAPTER-13

INTERACTING WITH DATABASES

Cursor is a method that provides a way to select multiple rows of data from the database and then process each row individually inside the PL/SQL program.

Types of Cursors :

♦ Implicit Cursor : Declared for all DML & PL/SQL SELECT statement including queries that return only one row.

♦ Explicit Cursor: For queries that return more than one row. Declared and named by programmer.

Explicit Cursor :

Following steps are followed when using the explicit cursor:

1. Declare the cursor.

2. Open the cursor.

3. Fetch the data from the cursor record by record.

4. Close the cursor.

Syntax for using cursor:

   ♦ Syntax of cursor declaration:

cursor is SQL select statement;

♦ Syntax of open statement:

open ;

♦ Syntax of fetch statement

fetch into var1,var2,var3…….

or

fetch into record_type_variable;

♦ Syntax of close statement:

close ;

Explicit Cursor attributes:
There are four cursor attributes :
♦ %ISOPEN : It returns true if cursor is open , otherwise it returns false.
Syntax : if cursorname%isopen then
……….
else
……….

endif

♦ %FOUND : It returns true if record was fetched properly from the cursor, otherwise it returns false.

Syntax : cursorname%found

♦ %NOTFOUND : It returns true if record is not successfully found, otherwise it returns false.

Syntax : cursorname%notfound

♦ %ROWCOUNT : It returns the no. of records processed by the cursor.

Syntax : cursorname%rowcount

Example code to illustrate cursor:

DECLARE

cursor empdis is SELECT * FROM emp;

e emp%ROWTYPE;

BEGIN

open empdis;

if empdis%ISOPEN then

dbms_output.put_line(‘empno name salary’);

LOOP

FETCH empdis into e;

EXIT WHEN empdis%notfound;

dbms_output.put_line(e.empno|| e.name|| e.sal);
ENDLOOP;
CLOSE empdis;
else
dbms_output.put_line(‘Cannot open the cursor’);

END IF;

END;

Implicit Cursors:

These are also called as SQL cursors.

PL/SQL employs implicit cursors for following statements:

i. INSERT

ii. UPDTAE

iii. DELETE

iv. SELECT(only those SELECT queries that return exactly one row.)

Subqueries,IN WHERE clause,IN FROM clause, Aliases, Expressions,bind variables can be used with

Explicit cursors.

Cursor Based Records:

Cursor FOR Loops:

In a Cursor FOR Loop,a declared cursor is OPENed,FETCHed and CLOSed automatically.

Syntax:

FOR IN

LOOP

END LOOP;

Cursor FOR Loop with Parameters:

Syntax:

FOR IN )

LOOP

.END LOOP;

Cursor FOR Loops Using Subqueries:

Syntax:

FOR IN (query_expression)

LOOP
.
END LOOP;

Please refer to attached file for CBSE Class 12 Informatics Practices Interacting with Databases study notes