rating trigger

Question

I need to create sql trigger if rating is more than 5 throw error

CREATE TRIGGER RATING_VALUE
BEFORE INSERT ON HOC_Reviews FOR EACH ROW
BEGIN
IF new.rating > 5 THEN
RAISERROR( "You can rate only from 1 to 5");
END IF;
END;/

Answer 1

That syntax looks like a mix of SQL Server and Oracle.

Anyway, that particular restriction is best implemented as a CHECK constraint:

ALTER TABLE HOC_reviews ADD ch_tbl_rating CHECK (rating BETWEEN 1 AND 5)

Key points for triggers in SQL Server:

• There are no BEFORE triggers. There are INSTEAD OF and AFTER triggers. The latter are easier to implement.
• A trigger once per statement; there is no per-row trigger.
• In a trigger for INSERT, you have access to the virtual table inserted, holds the newly inserted rows. The schema is the same as parent table for the trigger.
• Likewise, in trigger for DELETE, you have the virtual table deleted.
• And in a trigger for UPDATE, inserted holds the afterimage of the rows, and deleted has the beforeimage.

Answer 2

Hi @Kristína Juchová
As Erland said, there is no 'Before' Trigger in SQL Sever. However, in this issue, you can use FOR/AFTER triggers. Refer to this article for more details: CREATE TRIGGER (Transact-SQL)
Check this example:

IF OBJECT_ID('RATING_VALUE')IS NOT NULL  
DROP TRIGGER RATING_VALUE  
GO  
  
CREATE TRIGGER RATING_VALUE ON HOC_Reviews  
AFTER INSERT  
AS  
IF EXISTS(select 1 from inserted where RATING_VALUE not between 1 and 5)   
BEGIN    
   RAISERROR('You can rate only from 1 to 5',10,1)  
   ROLLBACK TRANSACTION;  
   RETURN  
END;   

In addition,you can also implement this: if rating value > 5, then set it to 5.
Like this:

IF OBJECT_ID('RATING_VALUE')IS NOT NULL  
DROP TRIGGER RATING_VALUE  
GO  
  
CREATE TRIGGER RATING_VALUE ON HOC_Reviews  
AFTER INSERT  
AS  
BEGIN    
   UPDATE HOC_Reviews SET RATING_VALUE = 5 WHERE RATING_VALUE > 5  
END;   

Best regards,
LiHong

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