There are Inserted and Deleted logical tables in SQL Server. These tables are automatically created and managed by SQL Server internally to hold recently inserted, deleted and updated values during DML operations (Insert,Update,Delete) on a database table.
Use of logical tables
Basically, logical tables are used by triggers for the following purpose:
To test data manipulation errors and take suitable actions based on the errors.
To find the difference between the state of a table before and after the data modification and take actions based on that difference.
Inserted logical Table
The Inserted table holds the recently inserted or updated values means new data values. Hence newly added and updated records are inserted into the Inserted table.
Suppose we have Employee table as shown in fig. Now We need to create two triggers to see data with in logical tables Inserted and Deleted.
CREATE TRIGGER trg_Emp_Ins ON Employee FOR INSERT AS begin SELECT * FROM INSERTED -- show data in Inserted logical table SELECT * FROM DELETED -- show data in Deleted logical table end
Now insert a new record in Employee table to see data with in Inserted logical table.
INSERT INTO Employee(EmpID, Name, Salary) VALUES(3,'Avin',23000) SELECT * FROM Employee
Deleted logical Table
The Deleted table holds the recently deleted or updated values means old data values. Hence old updated and deleted records are inserted into the Deleted table.
CREATE TRIGGER trg_Emp_Upd ON Employee FOR UPDATE AS begin SELECT * FROM INSERTED -- show data in INSERTED logical table SELECT * FROM DELETED -- show data in DELETED logical table end
--Now update the record in Employee table to see data with in Inserted and Deleted logical tables Update Employee set Salary=43000 where EmpID=3 SELECT * FROM Employee
We could not create the logical tables or modify the data with in the logical tables. Except triggers, When you use the OUTPUT clause in your query, logical tables are automatically created and managed by SQL Server. OUTPUT clause also has access to Inserted and Deleted logical tables just like triggers.
I hope you will enjoy these tips/tricks while programming with LINQ to SQL. I would like to have feedback from my blog readers. Your valuable feedback, question, or comments about this article are always welcome.