Fire SQL Trigger When Column Value Changes - sql-server

Question

I am adding the date to a column in SQL when the 'workstatus' is 'completed', but my problem is, when I open and save the same job again in the software, it runs the trigger and changes the date again to a new value which I don't want.
I want the trigger to run only if the 'workstatus' value is something else than 'completed'.
GO
/****** Object: Trigger [dbo].[TRJCD_JOBREQUEST] Script Date: 06/25/2021 15:49:04 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER TRIGGER [dbo].[TRJCD_JOBREQUEST] ON [dbo].[TBL_JOBREQUEST]
AFTER UPDATE,INSERT
AS
if (Update (workstatus))
begin
DECLARE #Jobcompletiondate datetime
DECLARE #workstatus VARCHAR(15)
DECLARE #jobid int
select #workstatus = workstatus from inserted
select #jobid = jobid from inserted
select #Jobcompletiondate = GETDATE()
begin
if #workstatus='Completed'
update TBL_JOBREQUEST set JobCompDate=#Jobcompletiondate where jobid = #jobid
end
end

Answer 1

The following is how you should construct your trigger.
There is no need to assign any values to variables, triggers fire once per batch and always operate on the set of updated rows.
If you update a status to Completed you need to check it's not currently Completed, also if you want to retain the first JobCompDate even if the status is amended afterwards simply use a case expression to only update the column where it's currently NULL.
create or alter trigger [dbo].[TRJCD_JOBREQUEST] on [dbo].[TBL_JOBREQUEST]
after update,insert
as
if ##RowCount=0 return
set nocount on
if Update (workstatus)
begin
update t set
t.JobCompDate=case when t.JobCompDate is null then GetDate() else t.JobCompDate end
from inserted i join TBL_JOBREQUEST t on t.jobid=i.jobid
where i.workstatus='Completed'
and not exists (
select * from deleted d
where d.jobid=i.jobid and d.workstatus=i.workstatus
)
end

Answer 2

Please note that I do not have your data set, so I'm unable to test the trigger, however, based on what you provided in your question, I believe this is the answer you are seeking:
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER TRIGGER [dbo].[TRJCD_JOBREQUEST] ON [dbo].[TBL_JOBREQUEST]
AFTER UPDATE,INSERT
AS
if (Update (workstatus))
begin
DECLARE #Jobcompletiondate datetime
DECLARE #currentworkstatus VARCHAR(15)
DECLARE #oldworkstatus VARCHAR(15)
DECLARE #jobid int
select #oldworkstatus = workstatus from deleted
select #currentworkstatus = workstatus from inserted
select #jobid = jobid from inserted
select #Jobcompletiondate = GETDATE()
begin
if #currentworkstatus='Completed' and #oldworkstatus <> 'Completed'
update TBL_JOBREQUEST set JobCompDate=#Jobcompletiondate where jobid = #jobid
end
end
You needed to check if the deleted workstatus does not equal Completed and only then should the trigger fire.