A Trigger is a SQL procedure that initiates an action when an events INSERT, DELETE , UPDATE occurs. Triggers are stored in and managed by the DBMS.Triggers are used to maintain the referential integrity of data by changing the data in a systematic fashion. A trigger cannot be called or executed; the DBMS automatically fires the trigger as a result of a data modification to the associated table. Triggers can be viewed as similar to stored procedures in that both consist of procedural logic that is stored at the database level. Stored procedures, however, are not event-driven and are not attached to a specific table as triggers. Stored procedures are explicitly executed by invoking the procedure while triggers are implicitly executed. In addition, triggers can also execute stored procedures.
Nested Trigger: A trigger can also contain INSERT, UPDATE and DELETE logic within itself, so when the trigger is fired because of data modification it can also cause another data modification, thereby firing another trigger. A trigger that contains data modification logic within itself is called a nested trigger.
Two types of Triggers
1) DML Trigger
DML is abbreviation of Data Manipulation Level. DML contains the actual data which is stored in the database schema. UPDATE, INSERT, DELETE, SELECT clause are used to manipulate database.
There are two types of DML Triggers
1.Instead of Trigger:- Instead of Triggers are fired in place of the triggering action such as an insert, update, delete.
2.After Trigger:- After triggers execute following the triggering action, such as an insert, update, delete.
2) DDL Trigger
DDL is abbreviation of Data Definition Level. DDL contains schema of the database object. It was always dream of all DBA, when change in mission critical schema of the database or server is attempted it is prevented immediately informing DBA and users automatically. DDL Trigger can now make this dream true. Definition of DDL Trigger is a special kind of trigger that fire in response to Data Definition Language (DDL) statements. They can be used to perform administrative tasks in the database such as auditing and regulating database operations.
Nested Trigger: A trigger can also contain INSERT, UPDATE and DELETE logic within itself, so when the trigger is fired because of data modification it can also cause another data modification, thereby firing another trigger. A trigger that contains data modification logic within itself is called a nested trigger.
Two types of Triggers
1) DML Trigger
DML is abbreviation of Data Manipulation Level. DML contains the actual data which is stored in the database schema. UPDATE, INSERT, DELETE, SELECT clause are used to manipulate database.
There are two types of DML Triggers
1.Instead of Trigger:- Instead of Triggers are fired in place of the triggering action such as an insert, update, delete.
2.After Trigger:- After triggers execute following the triggering action, such as an insert, update, delete.
2) DDL Trigger
DDL is abbreviation of Data Definition Level. DDL contains schema of the database object. It was always dream of all DBA, when change in mission critical schema of the database or server is attempted it is prevented immediately informing DBA and users automatically. DDL Trigger can now make this dream true. Definition of DDL Trigger is a special kind of trigger that fire in response to Data Definition Language (DDL) statements. They can be used to perform administrative tasks in the database such as auditing and regulating database operations.
