Triggers are stored procedures that are automatically executed in response to events like insert, update or delete on a table. There are two types of triggers - row triggers fired once per row affected and statement triggers fired once per SQL statement. Triggers can be before triggers fired before the event or after triggers fired after the event. Cursors allow processing of multiple rows returned by a select statement in PL/SQL as they provide a way to retrieve and process rows one by one. There are two types of cursors - implicit cursors created by Oracle for DML statements and explicit cursors created by the programmer for queries returning multiple rows which are opened, rows are fetched and processed, and then closed.

1. 1Using ORACLE®Triggers and Cursors

2. 2TriggersA trigger is a stored procedure that defines an action that the database automatically initiates when some database related event such as INSERT , UPDATE or DELETE occurs. when occurs fires a The main difference between a procedure and a trigger is that a procedure is executed explicitly from another block via a procedure call with arguments, while a trigger is executed implicitly when the triggering event like the occurrence of a DML-statement as INSERT ,UPDATE or DELETE occurs.Also a trigger does not accept arguments.The Automatic execution of triggers is known as firing of trigger.

3. 3Need and Types of TriggersNeed for triggers:Maintaining complex integrity constraints.Auditing the information in a table by recording the change.Automatically signaling another program about an occurred event.Enforcing complex business rules.

4. 4Need and Types of TriggersTypes of triggers:Row trigger: Fired once for every row that is affected.Statement trigger : Fired only once per statement regardless of the number of row affected.Before trigger: Fired before the triggering event occurs.After trigger: Fired after the triggering event occurs.

5. 5Syntax for TriggersSYNTAX :CREATE OR REPLACE TRIGGER trigger_name {BEFORE / AFTER } { INSERT / UPDATE / DELETE}ON object_name FOR { EACH ROW / EACH STATEMENT}BEGIN Statement1… ….. …...END;

6. 6Example for triggersSYNTAX :CREATE OR REPLACE TRIGGER trig AFTER DELETEON InfoTable FOR EACH ROWBEGIN INSERT INTO InfoTable VALUES(:old name,NULL,NULL);END; Using this trigger , whenever a row from the InfoTable will be deleted the trigger will be fired and the row containing the deleted row’s name will be inserted with other values as NULL which will help us identify later which rows were deleted.

7. 7NEED FOR CURSORSWe cannot use sub-programs of PL/SQL with a simple select statement to retrieve more than one row. If a select statement in a procedure returns more than one row ,Oracle returns an error message since PL/SQL requires a special compatibility to retrieve and process more than one row. Oracle processes procedure without error Oracle returns error.SELECT statement in procedure returning one rowrowSELECT statement in procedure returning more than one rowrowrowrow

8. 8CURSORA PL/SQL cursor is a mechanism that provides a way to select multiple rows of data from the database and then process each row individually inside a PL/SQL program. A cursor is basically an area of memory containing SQL statements and information for processing those statements.A CURSOR is a pointer to the context area. CURSOR is pointing at this row1 CURSOR is pointing at this row2 now The cursor first points at row1 and once it is processed it then advances to row2 and so on.row1row1row2row2row3row3row4row4

9. 9Types of CURSORSThere are two types of cursors:Implicit cursor: Created and used by Oracle for all DML and PL/SQL select statements including those returning only one row.Explicit cursor : Created and used by the programmer for queries that return more than one row.

10. 10Types of CURSORSSYNTAX:DECLARECURSOR cursor_name AS Cursor DeclarationSELECT statement;-- Variable declaration if any;BEGINOPEN cursor_name;FETCH <cursor_name> INTO <record_list> Cursor Body-- data fetched into active data set.CLOSE cursor_name;END;

11. 11EXAMPLE OF CURSORDECLARECURSOR cus AS SELECT * FROM InfoTable;customer InfoTable%ROWTYPE; declare a rowtype variableBEGINOPEN cus;LOOPFETCH cus into customer; Fetch the row into the variable and advance cursor.DBMS_OUTPUT.PUT_LINE(‘name:’||customer.name);DBMS_OUTPUT.PUT_LINE(‘age:’||customer.age);DBMS_OUTPUT.PUT_LINE(‘phone:’||customer.phone);EXIT WHEN cus%NOTFOUND; Returns true when all rows have been fetched.END LOOP;CLOSE cus;END;

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