What is a trigger in SQL? Why use triggers?
A trigger is a special kind of operations that execute automatically when an event occurs in the database (tables and views) when you trying to INSERT, UPDATE OR DELETE operations in the tables and views.
All the triggers are directly attached with the tables and views. Each of the tables has their own trigger.
Noted Points:-
1. We can’t create triggers against the system tables and views.
2. The AFTER triggers can’t be defined on the views.
3. You try to avoid using nested triggers.
4. You try to avoid using recursive triggers.
What types of trigger in SQL Server?
There are two types of Triggers available in the SQL that is
DML Triggers: - i) After Trigger ii) Instead of Trigger
DDL Triggers
There are three query actions that are used in SQL INSERT, UPDATE OR DELETE.
Syntax:-
--CREATE DATABASE TRIGGER TEMPLATE CREATE TRIGGER <trigger_name, sysname, table_alter_drop_safety> ON DATABASE FOR <data_definition_statements, , DROP_TABLE, ALTER_TABLE> AS IF IS_MEMBER ('db_owner') = 0 BEGIN PRINT 'You must ask your DBA to drop or alter tables!' ROLLBACK TRANSACTION END GO
How to create triggers?
--How to Create trigger? --CREATE TRIGGER CREATE TRIGGER myTrigger3 ON employee FOR UPDATE, INSERT, DELETE AS -- BEFORE INSERT SELECT 'Before INSERT' INSERT Employee (ID, Name) VALUES (31, 'Rick') GO --BEFORE UPDATE SELECT 'Before UPDATE' UPDATE Employee SET Name = 'Test' WHERE ID = 1 GO -- BEFORE DELETE SELECT 'Before DELETE' DELETE FROM Employee WHERE ID = 1
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