Question

I am findiing it hard to understand what this code is doing. Could someone please help me understand this code line by line so that I can understand what it is doing.

CREATE TRIGGER LowCredit ON Order
AFTER INSERT
AS

DECLARE @creditrating tinyint

SELECT @creditrating = v.CreditRating
FROM Customer c INNER JOIN inserted i
ON c.custID = i.custID

IF @creditrating = 5
BEGIN

    RAISERROR ('This customers''s credit rating
    is too low to accept new orders.’)

    ROLLBACK TRANSACTION

END

Answer 1

It is checking to see if the credit rating is a certain value, if its too low is raising an error and rolling back the transaction.

--Declare a trigger with name `LowCredit` on table `Order`, 
--run the trigger after 
CREATE TRIGGER LowCredit ON Order  
insert.
AFTER INSERT

AS
--start definition
--declare int
DECLARE @creditrating tinyint

--select from existing customer record the
-- inserted rows credit ranking (by custID)
-- inserted is the vt containing the changed rows
SELECT @creditrating = v.CreditRating
   FROM Customer c INNER JOIN inserted i
ON c.custID = i.custID
--if lower than 5 roll back
IF @creditrating = 5
BEGIN
--raise error to the session
RAISERROR ('This customers''s credit rating
is too low to accept new orders.’)
--roll back transaction
ROLLBACK TRANSACTION

END