How Can a SQL Server 2008 Trigger Ensure Employee Data Integrity in an EmployeeResult Table?

Using a Trigger to Ensure Employee Existence in EmployeeResult Table

SQL Server 2008 offers a powerful mechanism for enforcing data integrity and maintaining referential constraints through triggers. This article guides you through creating a simple INSERT trigger on the EmployeeResult table to address a common data consistency concern.

Understanding the Problem

The goal of the trigger is to ensure that every INSERT operation on the EmployeeResult table is accompanied by a corresponding entry in the Employee table, linking employee names and departments. If an existing employee is not found, the trigger inserts the necessary data into the Employee table.

Crafting the Trigger

To achieve this, we utilize the inserted logical table, which represents the data being inserted into the EmployeeResult table. The following trigger implementation accomplishes the desired behavior:

CREATE TRIGGER [trig_Update_Employee]
ON [EmployeeResult]
FOR INSERT
AS
BEGIN
    INSERT INTO [Employee] (Name, Department)
    SELECT DISTINCT i.name, i.Department
    FROM inserted AS i
    LEFT JOIN Employee e
    ON i.Name = e.Name AND i.Department = e.Department
    WHERE e.Name IS NULL;
END

Explaining the Solution

• Line 1: The trigger name is declared as [trig_Update_Employee].
• Line 2: The trigger is applied to the [EmployeeResult] table.
• Line 3: The trigger executes whenever an INSERT occurs on the table.
• Line 5: We use the inserted logical table and DISTINCT to prevent duplicate entries.
• Lines 6-8: We perform a LEFT JOIN with the Employee table to identify missing employees and departments.

Benefits of the Trigger

• Ensures data integrity by maintaining referential integrity between EmployeeResult and Employee tables.
• Simplifies data entry by automatically adding new employees to the Employee table, reducing the potential for errors.
• Enhances data consistency by guaranteeing that employee information is present in both tables.

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