![\"What](\"https:\/\/openquery.com\/wp-content\/uploads\/2022\/02\/What-Is-A-Trigger-In-SQL-1024x683.png\")
<\/figure><\/div>\n\n\n\nWhat Is The Purpose Of A SQL Trigger?<\/strong><\/h2>\n\n\n\nThe purpose of a SQL trigger is to maintain referential integrity of any given data by altering the data systematically. <\/p>\n\n\n\n
At any time, a trigger is connected to a single, specific table within a database. That being said, there can be any number of triggers associated with any table within a database. <\/p>\n\n\n\n
As they are managed by a DBMS, triggers cannot be called or executed, they are automatically fired whenever data is modified within it\u2019s connected table. <\/p>\n\n\n\n
We mentioned in the introduction that a SQL can be thought of as a specific type of stored procedure. Whilst there are some similarities between stored procedures and triggers, there are also some key differences. <\/p>\n\n\n\n
The main similarity is that, on a database level, they both contain procedural logic. <\/p>\n\n\n\n
Stored procedures tend to be passive, in a sense that they are not event-driven. They are also not connected to any specific table within the database, unlike triggers. <\/p>\n\n\n\n
Stored procedures are explicitly executed (meaning that there is an intention to execute a stored procedure) by using a CALL to a specific procedure. In this sense, triggers are passive, as they are implicitly executed as a result of particular clauses being executed. <\/p>\n\n\n\n
What Are 3 Types Of SQL Triggers?\u00a0<\/strong><\/h2>\n\n\n\nAs mentioned above, triggers are managed by a DBMS and as such are outside of interference. <\/p>\n\n\n\n
If any of the three clauses below are executed within a database, a SQL trigger will fire: <\/p>\n\n\n\n
UPDATE, INSERT, DELETE<\/p>\n\n\n\n
Each of these clauses can be used to modify data within a given table in a database. <\/p>\n\n\n\n
UPDATE: is used to modify existing values <\/p>\n\n\n\n
INSERT: is used to add new rows within a table <\/p>\n\n\n\n
DELETE: is used to remove rows from a table<\/p>\n\n\n\n
In certain situations, triggers can contain the above (UPDATE, INSERT, DELETE) logic within itself. This means that if a trigger is fired, say because of a modification to data, it will cause a second data modification and fire another trigger. This is known as a nested trigger. <\/p>\n\n\n\n
The Three Groups of Triggers<\/strong><\/h2>\n\n\n\nDDL Trigger <\/strong><\/h3>\n\n\n\nDDL stands for Data Definition Language. A DDL Trigger will usually fire as a response to DDL events within a database. <\/p>\n\n\n\n
They are commands which start with Create, Alter, Drop, Deny, Revoke, Grant, or Update Statistics, for example Create_view, Drop_table, Alter_table. <\/p>\n\n\n\n
DDL triggers are applicable if you want to do the following: <\/p>\n\n\n\n
DML Trigger<\/strong><\/h3>\n\n\n\nDML is an acronym for Data Manipulation Language. DML triggers are fired as a response to command events that start with Insert, Update, and Delete statements. <\/p>\n\n\n\n
In terms of application, DML triggers are used to query other tables, enforce business rules\/data integrity, and include Transact-SQL statements. <\/p>\n\n\n\n
There are two types of DML triggers which fall under the DML banner. These are AFTER triggers and INSTEAD OF triggers. <\/p>\n\n\n\n
After Triggers are executable after the action of Insert, Update, or Delete statements. <\/p>\n\n\n\n
Using an Instead Of Trigger tells the database to execute a trigger instead of a statement. An example of this is an insert trigger will execute when an event occurs instead of the statement that would place values in the table. <\/p>\n\n\n\n
Logon Trigger<\/strong><\/h3>\n\n\n\nAs the name suggests, this trigger fires stored procedures in response to a Logon event. Usually, this event is raised whenever a user session is established with an instance of SQL Server<\/a>. They fire post authentication phase of logging in, but pre user session establishment. <\/p>\n\n\n\nTheir most common application is to audit and control server sessions, by tracking login activity, restricting logins, or limiting the number of sessions for a particular login. <\/p>\n\n\n\n
When Might You Use SQL Triggers?\u00a0<\/strong><\/h2>\n\n\n\nAs we\u2019ve mentioned earlier, triggers have a lot in common with stored procedures. However, when compared to a stored procedure, they are limited in what triggers can do. <\/p>\n\n\n\n
With this in mind, it could be easier to maintain one stored procedure for any Insert, Update, or Delete clauses and make checks\/add additional actions there. <\/p>\n\n\n\n
The big caveat to this is that this isn\u2019t always possible. If, for example, you inherited a system or simply do not want to put all the logic in one stored procedure, triggers can be a solution for many problems you might encounter.<\/p>\n\n\n\n
In Summary<\/strong><\/h2>\n\n\n\nA SQL Trigger\u2019s main function is to maintain referential integrity of any given data by making changes to the data systematically. <\/p>\n\n\n\n
They cannot be called or executed, as they are automatically executed whenever data is modified. <\/p>\n\n\n\n
There are three main groups of triggers: DDL, DML, and LOGON. <\/p>\n\n\n\n
Within DML, there are two subcategories which are worth repeating: After Triggers and Instead Of Triggers. <\/p>\n\n\n\n
A Trigger in SQL is a procedure which runs automatically whenever there is an event within the database.\u00a0<\/p>\n\n\n\n
As mentioned above, triggers are managed by a DBMS and as such are outside of interference. <\/p>\n\n\n\n
If any of the three clauses below are executed within a database, a SQL trigger will fire: <\/p>\n\n\n\n
UPDATE, INSERT, DELETE<\/p>\n\n\n\n
Each of these clauses can be used to modify data within a given table in a database. <\/p>\n\n\n\n
UPDATE: is used to modify existing values <\/p>\n\n\n\n
INSERT: is used to add new rows within a table <\/p>\n\n\n\n
DELETE: is used to remove rows from a table<\/p>\n\n\n\n
In certain situations, triggers can contain the above (UPDATE, INSERT, DELETE) logic within itself. This means that if a trigger is fired, say because of a modification to data, it will cause a second data modification and fire another trigger. This is known as a nested trigger. <\/p>\n\n\n\n
The Three Groups of Triggers<\/strong><\/h2>\n\n\n\nDDL Trigger <\/strong><\/h3>\n\n\n\nDDL stands for Data Definition Language. A DDL Trigger will usually fire as a response to DDL events within a database. <\/p>\n\n\n\n
They are commands which start with Create, Alter, Drop, Deny, Revoke, Grant, or Update Statistics, for example Create_view, Drop_table, Alter_table. <\/p>\n\n\n\n
DDL triggers are applicable if you want to do the following: <\/p>\n\n\n\n
DML Trigger<\/strong><\/h3>\n\n\n\nDML is an acronym for Data Manipulation Language. DML triggers are fired as a response to command events that start with Insert, Update, and Delete statements. <\/p>\n\n\n\n
In terms of application, DML triggers are used to query other tables, enforce business rules\/data integrity, and include Transact-SQL statements. <\/p>\n\n\n\n
There are two types of DML triggers which fall under the DML banner. These are AFTER triggers and INSTEAD OF triggers. <\/p>\n\n\n\n
After Triggers are executable after the action of Insert, Update, or Delete statements. <\/p>\n\n\n\n
Using an Instead Of Trigger tells the database to execute a trigger instead of a statement. An example of this is an insert trigger will execute when an event occurs instead of the statement that would place values in the table. <\/p>\n\n\n\n
Logon Trigger<\/strong><\/h3>\n\n\n\nAs the name suggests, this trigger fires stored procedures in response to a Logon event. Usually, this event is raised whenever a user session is established with an instance of SQL Server<\/a>. They fire post authentication phase of logging in, but pre user session establishment. <\/p>\n\n\n\nTheir most common application is to audit and control server sessions, by tracking login activity, restricting logins, or limiting the number of sessions for a particular login. <\/p>\n\n\n\n
When Might You Use SQL Triggers?\u00a0<\/strong><\/h2>\n\n\n\nAs we\u2019ve mentioned earlier, triggers have a lot in common with stored procedures. However, when compared to a stored procedure, they are limited in what triggers can do. <\/p>\n\n\n\n
With this in mind, it could be easier to maintain one stored procedure for any Insert, Update, or Delete clauses and make checks\/add additional actions there. <\/p>\n\n\n\n
The big caveat to this is that this isn\u2019t always possible. If, for example, you inherited a system or simply do not want to put all the logic in one stored procedure, triggers can be a solution for many problems you might encounter.<\/p>\n\n\n\n
In Summary<\/strong><\/h2>\n\n\n\nA SQL Trigger\u2019s main function is to maintain referential integrity of any given data by making changes to the data systematically. <\/p>\n\n\n\n
They cannot be called or executed, as they are automatically executed whenever data is modified. <\/p>\n\n\n\n
There are three main groups of triggers: DDL, DML, and LOGON. <\/p>\n\n\n\n
Within DML, there are two subcategories which are worth repeating: After Triggers and Instead Of Triggers. <\/p>\n\n\n\n
A Trigger in SQL is a procedure which runs automatically whenever there is an event within the database.\u00a0<\/p>\n\n\n\n
DDL stands for Data Definition Language. A DDL Trigger will usually fire as a response to DDL events within a database. <\/p>\n\n\n\n
They are commands which start with Create, Alter, Drop, Deny, Revoke, Grant, or Update Statistics, for example Create_view, Drop_table, Alter_table. <\/p>\n\n\n\n
DDL triggers are applicable if you want to do the following: <\/p>\n\n\n\n
DML Trigger<\/strong><\/h3>\n\n\n\nDML is an acronym for Data Manipulation Language. DML triggers are fired as a response to command events that start with Insert, Update, and Delete statements. <\/p>\n\n\n\n
In terms of application, DML triggers are used to query other tables, enforce business rules\/data integrity, and include Transact-SQL statements. <\/p>\n\n\n\n
There are two types of DML triggers which fall under the DML banner. These are AFTER triggers and INSTEAD OF triggers. <\/p>\n\n\n\n
After Triggers are executable after the action of Insert, Update, or Delete statements. <\/p>\n\n\n\n
Using an Instead Of Trigger tells the database to execute a trigger instead of a statement. An example of this is an insert trigger will execute when an event occurs instead of the statement that would place values in the table. <\/p>\n\n\n\n
Logon Trigger<\/strong><\/h3>\n\n\n\nAs the name suggests, this trigger fires stored procedures in response to a Logon event. Usually, this event is raised whenever a user session is established with an instance of SQL Server<\/a>. They fire post authentication phase of logging in, but pre user session establishment. <\/p>\n\n\n\nTheir most common application is to audit and control server sessions, by tracking login activity, restricting logins, or limiting the number of sessions for a particular login. <\/p>\n\n\n\n
When Might You Use SQL Triggers?\u00a0<\/strong><\/h2>\n\n\n\nAs we\u2019ve mentioned earlier, triggers have a lot in common with stored procedures. However, when compared to a stored procedure, they are limited in what triggers can do. <\/p>\n\n\n\n
With this in mind, it could be easier to maintain one stored procedure for any Insert, Update, or Delete clauses and make checks\/add additional actions there. <\/p>\n\n\n\n
The big caveat to this is that this isn\u2019t always possible. If, for example, you inherited a system or simply do not want to put all the logic in one stored procedure, triggers can be a solution for many problems you might encounter.<\/p>\n\n\n\n
In Summary<\/strong><\/h2>\n\n\n\nA SQL Trigger\u2019s main function is to maintain referential integrity of any given data by making changes to the data systematically. <\/p>\n\n\n\n
They cannot be called or executed, as they are automatically executed whenever data is modified. <\/p>\n\n\n\n
There are three main groups of triggers: DDL, DML, and LOGON. <\/p>\n\n\n\n
Within DML, there are two subcategories which are worth repeating: After Triggers and Instead Of Triggers. <\/p>\n\n\n\n
A Trigger in SQL is a procedure which runs automatically whenever there is an event within the database.\u00a0<\/p>\n\n\n\n
As the name suggests, this trigger fires stored procedures in response to a Logon event. Usually, this event is raised whenever a user session is established with an instance of SQL Server<\/a>. They fire post authentication phase of logging in, but pre user session establishment. <\/p>\n\n\n\n Their most common application is to audit and control server sessions, by tracking login activity, restricting logins, or limiting the number of sessions for a particular login. <\/p>\n\n\n\n As we\u2019ve mentioned earlier, triggers have a lot in common with stored procedures. However, when compared to a stored procedure, they are limited in what triggers can do. <\/p>\n\n\n\n With this in mind, it could be easier to maintain one stored procedure for any Insert, Update, or Delete clauses and make checks\/add additional actions there. <\/p>\n\n\n\n The big caveat to this is that this isn\u2019t always possible. If, for example, you inherited a system or simply do not want to put all the logic in one stored procedure, triggers can be a solution for many problems you might encounter.<\/p>\n\n\n\n A SQL Trigger\u2019s main function is to maintain referential integrity of any given data by making changes to the data systematically. <\/p>\n\n\n\n They cannot be called or executed, as they are automatically executed whenever data is modified. <\/p>\n\n\n\n There are three main groups of triggers: DDL, DML, and LOGON. <\/p>\n\n\n\n Within DML, there are two subcategories which are worth repeating: After Triggers and Instead Of Triggers. <\/p>\n\n\n\n A Trigger in SQL is a procedure which runs automatically whenever there is an event within the database.\u00a0<\/p>\n\n\n\nWhen Might You Use SQL Triggers?\u00a0<\/strong><\/h2>\n\n\n\n
In Summary<\/strong><\/h2>\n\n\n\n