Trigger: Automatically signalling the other programs that an

Trigger:

Trigger is same like a stored procedures where we can write
SQL code and save it which gets executed automatically whenever an event takes
place on the associated database.  We
cannot call triggers directly. There are 2 steps that are required for writing
a trigger.

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1.      
Firstly we must mention when the trigger has to
be executed like. Such that this is considered as an event and checks the
trigger and whether it satisfies the given condition for which the trigger has
to execute.

2.      
Now we have to mention the actions that has to
take place when the trigger is executed.

Uses of Triggers:

1.      
Triggers are used to maintain the complex
integrity constraints which are not possible at the time of table creation.

2.      
Automatically signalling the other programs that
an action needs to be take place when changes are made to a table.

3.      
Used to implement specific business rules.

 

Types of Triggers:

1.      
DML Triggers

2.      
DDL Triggers

3.      
Logon Triggers

DML triggers:

DML triggers will be executed automatically whenever a data
manipulation operations (insertion, deletion, updating) take place on the table
or view which is mentioned in the trigger. DML triggers are classified into two
types.

1.      
After Trigger

2.      
INSTEAD OF trigger

After Trigger: These types of triggers are fired only after
the execution of DML operations and before the committing the data into the
database.  We cannot apply after trigger
on views.

For example: Create an after trigger for update operation.
Now if you execute update statement then after the execution the after trigger
is fired before the update statement is committed.

INSTEADOF trigger: INSTEAD OF trigger is executed in place
of insert, delete, and update. The actual insert, delete and update are not
included in the table.

For example: suppose if you have INSTEAD of trigger for
update operation. Then If we give an update operation so before the update
operation the instead of trigger for update is raised and it will execute in
place of update operation.

Uses of DML Triggers:

1.      
DML triggers are same as constraints which
enforce the data integrity.

2.      
A normal constraint in the SQL gives a standard
system error message when an issue occurs. In order to customize the message
and to handle more complex error-handling DML triggers are used.

3.      
To perform multiple actions for the same event
we can create more than one trigger using DML triggers.

DDL Triggers:

These type of triggers are fired when any of the DDL
statements are executed i.e.; DDL events occurred like when creation, alteration,
granting permission, denning permissions, dropping, Revoke permissions.

The scope of the DDL triggers:

We can create the DDL triggers in a particular database or
at the server level. So when you create a DDL trigger we must specify whether
it is database level or server level by ON DATABASE clause or ON ALL SERVER
clause respective.  Database level means when
creating a table, procedure, functions and altering a table, procedure and function
in a database. Server level means when creating a login, database, altering the
database, login and dropping the login, granting the server etc.

Unlike the DML triggers DDL triggers doesn’t contain the
INSTEAD OF trigger. If a global temporary tables and stored procedures are
affected by an event then DDL Trigger will not fire.

Uses of DDL Triggers:

1.      
By using DDL triggers we can place restrictions
on a user’s who are going to attempt to create, alter, and drop the database
objects.

2.      
Used to record the changes that take place in
the database schema.

 

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