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Sunday, November 9, 2014
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Implementing Triggers and its Types in SQL

8:46 AMSunday, November 9, 2014
In a relational database, data in a table is related to other tables. Therefore, while manipulating data in one table, you need to verify and validate its effect on data in the related tables. In addition, you might need to manipulate data in a table after inserting or updating data in another table.

You also need to ensure that if an error occurs while updating the data in a table, the changes are reverted. This helps in maintaining data integrity. The SQL Server allows you to implement triggers and transactions to maintain data integrity.

This article explains different types of triggers that can be created in SQL Server. Next, we will discusses how to implement triggers to enforce data integrity. Further, we will discuss about how to implement transactions.

Implement Triggers

At times, while performing data manipulation on a database object, you might also need to perform another manipulation on another object. For example, in an organization, the employees use the Online Leave Approval system to apply for leaves. When an employee applies for a leave, the leave details are stored in the Leave-Details table. In addition, a new record is added to the Leaves-For-Approval table. When the supervisors log on to the system, all the leaves pending for their approval are retrieved from the Leaves-For-Approval table and displayed to them.

To perform such operations, the SQL Server allows you to implement triggers. A trigger is a block of code that constitutes a set of T-SQL statements activated in response to certain actions, such as insert or delete. Triggers are used to ensure data integrity before or after performing data manipulations.

Before you implement a trigger, it is important to know the different types of triggers that can be created by using SQL Server.

Identifying Types of Triggers

In the SQL Server, various kinds of triggers can be used for different types of data manipulation operations. The SQL Server supports the following types of triggers:

Data Modification Language (DML) triggers

A DML trigger is fired when data in the underlying table is affected by DML statements, such as INSERT, UPDATE, or DELETE. These triggers help in maintaining consistent, reliable, and correct data in tables. They enable the performance of complex action and cascade these actions to other dependent tables. Cascading is the process of reflecting the changes made in a table in the other related tables.

Data Definition Language (DDL) triggers

A DDL trigger is fired in response to DDL statements, such as CREATE TABLE or ALTER TABLE. DDL triggers can be used to perform administrative tasks, such as database auditing.

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