Check business logic in a trigger : Trigger « Trigger « SQL Server / T-SQL Tutorial

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SQL Server / T-SQL Tutorial » Trigger » Trigger 
22. 1. 10. Check business logic in a trigger
2>
3CREATE TABLE Products (
4>      ProductID int IDENTITY (11NOT NULL ,
5>      ProductName nvarchar (40NOT NULL ,
6>      SupplierID int NULL ,
7>      CategoryID int NULL ,
8>      QuantityPerUnit nvarchar (20NULL ,
9>      UnitPrice money NULL,
10>     UnitsInStock smallint NULL,
11>     UnitsOnOrder smallint NULL,
12>     ReorderLevel smallint NULL,
13>     Discontinued bit NOT NULL
14)
15> GO
1>    CREATE TRIGGER ProductIsRationed
2>       ON Products
3>       FOR UPDATE
4>    AS
5>       IF EXISTS
6>          (
7>           SELECT 'True'
8>           FROM Inserted i
9>           JOIN Deleted d
10>              ON i.ProductID = d.ProductID
11>           WHERE (d.UnitsInStock - i.UnitsInStock> d.UnitsInStock / 2
12>              AND d.UnitsInStock - i.UnitsInStock > 0
13>          )
14>       BEGIN
15>          RAISERROR('Cannot reduce stock by more than 50%% at once.',16,1)
16>          ROLLBACK TRAN
17>       END
18>       GO
1>
2> drop TRIGGER ProductIsRationed;
3> GO
1>
2> drop table Products;
3> GO
1>
22. 1. Trigger
22. 1. 1. The syntax of the CREATE TRIGGER statement
22. 1. 2. exits if the price column has not been updated.
22. 1. 3. Define variables in a trigger
22. 1. 4. Update table in a trigger
22. 1. 5. Check @@ROWCOUNT in a trigger
22. 1. 6. Rollback transaction in a trigger
22. 1. 7. RAISERROR in trigger
22. 1. 8. Disable a trigger
22. 1. 9. Enable a trigger
22. 1. 10. Check business logic in a trigger
22. 1. 11. Check record matching in a trigger
22. 1. 12. Table for INSTEAD OF Trigger for Logical Deletes
22. 1. 13. INSTEAD OF INSERT trigger for a table
22. 1. 14. Trigger Scripts for Cascading DELETEs
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