SQL触发器检查以前的值

Question

I have a trigger on table tblA if the status is closed it inserts a record to table tblB . The below code is working, but I want it to be executed only if the previous status was NOT closed . How can I check it?

ON tblA
AFTER UPDATE
AS
  BEGIN
    SET NOCOUNT ON
    INSERT INTO tblB 
        (a_id, action, usr)
        select a.ID, 'closed', a.usr
        from tblA a
    WHERE a.Status LIKE 'closed';  
    END

Answer 1

A trigger in SQL Server is always suspect if it fails to access either inserted or deleted (or both), since those are the pseudo-tables that give you the details of what changed .

You want something like:

INSERT INTO tblB 
    (a_id, action, usr)
    select a.ID, 'closed', a.usr
    from inserted a
            inner join
         deleted d
            on a.ID = d.ID
WHERE a.Status = 'closed'
  AND d.Status != 'closed';