PLSQL Cursor with example

PLSQL Cursor:

A cursor is a pointer to this context area. PL/SQL controls the context area through a cursor. A cursor holds the rows (one or more) returned by a SQL statement. The set of rows the cursor holds is referred to as the active set.

There are two types of cursors:

·         Implicit cursors

·         Explicit cursors

Implicit Cursor: Implicit cursors are automatically created by Oracle whenever an SQL statement is executed, when there is no explicit cursor for the statement. Programmers cannot control the implicit cursors and the information in it.

Whenever a DML statement (INSERT, UPDATE and DELETE) is issued, an implicit cursor is associated with this statement. For INSERT operations, the cursor holds the data that needs to be inserted. For UPDATE and DELETE operations, the cursor identifies the rows that would be affected.

Attribute of Implicit Cursor:

Attribute	Description
%FOUND	Returns TRUE if an INSERT, UPDATE, or DELETE statement affected one or more rows or a SELECT INTO statement returned one or more rows. Otherwise, it returns FALSE.
%NOTFOUND	The logical opposite of %FOUND. It returns TRUE if an INSERT, UPDATE, or DELETE statement affected no rows, or a SELECT INTO statement returned no rows. Otherwise, it returns FALSE.
%ISOPEN	Always returns FALSE for implicit cursors, because Oracle closes the SQL cursor automatically after executing its associated SQL statement.
%ROWCOUNT	Returns the number of rows affected by an INSERT, UPDATE, or DELETE statement, or returned by a SELECT INTO statement.

Example: The following program would update the table and increase salary of each customer by 500 and use the SQL%ROWCOUNT attribute to determine the number of rows affected:

DECLARE

   total_rows number(2);

BEGIN

   UPDATE customers

   SET salary = salary + 500;

   IF sql%notfound THEN

      dbms_output.put_line('no customers selected');

   ELSIF sql%found THEN

      total_rows := sql%rowcount;

      dbms_output.put_line( total_rows || ' customers selected ');

   END IF;

END;

/

Result:

6 customers selected

PL/SQL procedure successfully completed.

Explicit Cursor: Explicit cursors are programmer defined cursors for gaining more control over the context area. An explicit cursor should be defined in the declaration section of the PL/SQL Block. It is created on a SELECT Statement which returns more than one row.

Explicit cursor involves four steps:

·         Declaring the cursor for initializing in the memory

·         Opening the cursor for allocating memory

·         Fetching the cursor for retrieving data

·         Closing the cursor to release allocated memory

Example:

DECLARE

   c_id customers.id%type;

   c_name customers.name%type;

   c_addr customers.address%type;

   CURSOR c_customers is

      SELECT id, name, address FROM customers;

BEGIN

   OPEN c_customers;

   LOOP

      FETCH c_customers into c_id, c_name, c_addr;

      EXIT WHEN c_customers%notfound;

      dbms_output.put_line(c_id || ' ' || c_name || ' ' || c_addr);

   END LOOP;

   CLOSE c_customers;

END;

/

Result:

1 Ramesh Ahmedabad 

2 Khilan Delhi 

3 kaushik Kota    

4 Chaitali Mumbai 

5 Hardik Bhopal  

6 Komal MP  

PL/SQL procedure successfully completed.