Update table with SET command IF / ELSE - sql-server

Question

I'm trying to update a table and i want to runt 2 different SET senarios depending on a stock value.
Working CODE that does one senario.
UPDATE dbo.ar
SET webPublish = '0',
ArtProdKlass = '9999',
VaruGruppKod = '9999',
ItemStatusCode = '9' --Utgått ur sortimentet+
FROM tmp_9999
WHERE ar.ArtNr = tmp_9999.art AND ar.lagsadloartikel < '1'
What i would like to do is that IF last statement (ar.lagsaldoartikel) is >'1'Then i would like it to run this SET:
SET webPublish = '1',
ArtProdKlass = '1',
VaruGruppKod = '9999',
ItemStatusCode = '8'
So something like this i have tested:
IF AR.lagsaldoartikel < '1'
SET webPublish = '0',
ArtProdKlass = '9999',
VaruGruppKod = '9999',
ItemStatusCode = '9' --Utgått ur sortimentet+
FROM tmp_9999
WHERE ar.ArtNr = tmp_9999.art --Väljer ut artiklar som enbart finns i textfilen och har lagersaldo mindre än 1
ELSE
SET webPublish = '1',
ArtProdKlass = '1',
VaruGruppKod = '9999',
ItemStatusCode = '8' --Utgått ur sortimentet
FROM tmp_9999
WHERE ar.ArtNr = tmp_9999.art --Väljer ut artiklar som enbart finns i textfilen och har lagersaldo mindre än 1

Answer 1

Using CASE:
UPDATE dbo.ar
SET webPublish = '0',
ArtProdKlass = '9999',
VaruGruppKod = '9999',
ItemStatusCode = CASE WHEN AR.lagsaldoartikel < '1' THEN '9' ELSE '8' END
FROM tmp_9999
WHERE ar.ArtNr = tmp_9999.art
(If ItemStatusCode et al are numeric you should treat them as such.)

Answer 2

If is part of the procedural T-SQL. You can't use procedural statements inside the relational ones - the only way to use if would be to have two separate update statements, each in one branch of the if. However, that's a bad idea - it's not concurrency-safe.
One way to accomplish what you're trying to do is to use the case statement instead - that's just an expression, so it can be used in the set clause just fine:
set webPublish = case when AR.lagsaldoartikel < '1' then '0' else '1' end
(etc. for the other arguments).
However, I'd like to warn you - this is almost certainly a bad idea. It's probably going to back-fire on you soon in the future, when you realize that there's ten different conditions and a hundred different possible values you might want. Consider using a more idiomatically relational way of doing this - for example, taking the conditions and arguments from a different table - it's not necessary now, but if you ever find your conditions are expanding out of reasonable size, remember to consider changing the whole structure of the command if needed.