SQL Server : trigger how to read value for Insert, Update, Delete

Question

I have the trigger in one table and would like to read UserId value when a row is inserted, updated or deleted. How to do that? The code below does not work, I get error on UPDATED

ALTER TRIGGER [dbo].[UpdateUserCreditsLeft]     ON  [dbo].[Order]    AFTER INSERT,UPDATE,DELETE AS  BEGIN     -- SET NOCOUNT ON added to prevent extra result sets from     -- interfering with SELECT statements.     SET NOCOUNT ON;      DECLARE      @UserId INT,      SELECT @UserId = INSERTED.UserId FROM INSERTED, DELETED      UPDATE dbo.[User] SET CreditsLeft = CreditsLeft - 1 WHERE Id = @UserId END 

Answer 1

Please note that inserted, deleted means the same thing as inserted CROSS JOIN deleted and gives every combination of every row. I doubt this is what you want.

Something like this may help get you started...

SELECT   CASE WHEN inserted.primaryKey IS NULL THEN 'This is a delete'        WHEN  deleted.primaryKey IS NULL THEN 'This is an insert'                                         ELSE 'This is an update'   END  as Action,   * FROM   inserted FULL OUTER JOIN   deleted     ON inserted.primaryKey = deleted.primaryKey 

Depending on what you want to do, you then reference the table you are interested in with inserted.userID or deleted.userID, etc.

Finally, be aware that inserted and deleted are tables and can (and do) contain more than one record.

If you insert 10 records at once, the inserted table will contain ALL 10 records. The same applies to deletes and the deleted table. And both tables in the case of an update.

EDIT Examplee Trigger after OPs edit.

ALTER TRIGGER [dbo].[UpdateUserCreditsLeft]    ON  [dbo].[Order]   AFTER INSERT,UPDATE,DELETE AS  BEGIN    -- SET NOCOUNT ON added to prevent extra result sets from   -- interfering with SELECT statements.   SET NOCOUNT ON;    UPDATE     User   SET     CreditsLeft = CASE WHEN inserted.UserID IS NULL THEN <new value for a  DELETE>                        WHEN  deleted.UserID IS NULL THEN <new value for an INSERT>                                                     ELSE <new value for an UPDATE>                   END   FROM     User   INNER JOIN     (       inserted     FULL OUTER JOIN       deleted         ON inserted.UserID = deleted.UserID  -- This assumes UserID is the PK on UpdateUserCreditsLeft     )       ON User.UserID = COALESCE(inserted.UserID, deleted.UserID)  END 

If the PrimaryKey of UpdateUserCreditsLeft is something other than UserID, use that in the FULL OUTER JOIN instead.