SQL Server - using variable in triggers - sql

Question

I have a trigger set on a table to run after Insert and I want to query the incoming data with that already in the target table, then append a different message based on the changes identified.
Here's what I have so far
ALTER TRIGGER [dbo].[trg_Measure_Insert_Audit]
ON [dbo].[Measures_slave]
AFTER INSERT
AS
BEGIN
SET NOCOUNT ON;
DECLARE #message VARCHAR(MAX)
insert into aud_Measures
(
measure_FK,
[description],
oldname,
[newname],
milestone
)
select
i.measure_PK,
CASE
WHEN (SELECT TOP 1 measure_name FROM Measures_slave s WHERE s.slave_PK = i.slave_PK -1) <> i.measure_name THEN 'Measure Name Changed to <b> ' + i.measure_name + ' </b>'
END,
(SELECT TOP 1 measure_name FROM Measures_slave s WHERE s.slave_PK = i.slave_PK -1),
i.measure_name,
--'Test Audit Entry',
'Yes'
from
inserted i
END
I want to replace the CASE WHEN with a list of either IFs or WHENs that go down each field on both measure_slave and Inserted and append a message to #message if a difference is found.
I'm trying to achieve this, essentially:
select
i.measure_PK,
CASE
--WHEN (SELECT TOP 1 measure_name FROM Measures_slave s WHERE s.slave_PK = i.slave_PK -1) <> i.measure_name THEN 'Measure Name Changed to <b> ' + i.measure_name + ' </b>'
WHEN (SELECT TOP 1 measure_name FROM Measures_slave s WHERE s.slave_PK = i.slave_PK -1) <> i.measure_name SET #message = 'Measure Name Changed to <b> ' + i.measure_name + ' </b>'
WHEN (SELECT TOP 1 calculation_steps FROM Measures_slave s WHERE s.slave_PK = i.slave_PK -1) <> i.calculation_steps SET #message = #message + 'Steps changed to: <b> ' + i.calculation_steps + ' </b>'
END,
(SELECT TOP 1 measure_name FROM Measures_slave s WHERE s.slave_PK = i.slave_PK -1),
i.measure_name,
--'Test Audit Entry',
'Yes'
from
inserted i

Answer 1

I think you may be able to achive what you need without using a variable:
ALTER TRIGGER [dbo].[trg_Measure_Insert_Audit]
ON [dbo].[Measures_slave]
AFTER INSERT
AS
BEGIN
SET NOCOUNT ON;
INSERT INTO aud_Measures
(
measure_FK,
[description],
oldname,
[newname],
milestone
)
SELECT
i.measure_PK,
CASE WHEN (i.measure_name <> s.measure_name) THEN 'Measure Name Changed to <b> ' + i.measure_name + ' </b>' ELSE '' END + -- The resulting value from this line concatenates with
CASE WHEN (i.calculation_steps <> s.calculation_steps ) THEN 'Steps changed to: <b> ' + i.calculation_steps + ' </b>' ELSE '' END, -- the resulting value from of this line
s.measure_name,
i.measure_name
'Yes'
FROM Inserted i LEFT JOIN Measures_slave s ON s.slave_PK = i.slave_PK -1
-- If you want to audit only the rows that in which there IS actually a difference in any of measure_name or calculation_steps columns, then use the following:
WHERE (i.measure_name <> s.measure_name) OR (i.calculation_steps <> s.calculation_steps )
END