using CASE in SQL with update statement

Question

I am trying to write a case statement something like this. Can someone help with the syntax

UPDATE A
CASE WHEN ATTDESC = 'ABC' THEN SET A.DESC = PG.VAL + ' - ' + LD.DESC + ' - ' + GH.PL3NAME
     WHEN ATTDESC = 'DEF' THEN SET A.DESC = PG.VAL + ' - ' + LD.DESC + ' - ' + GH.PL3NAME
END
FROM ATTR A, PRODUCT PG, Global GH, Look LD

Answer 1

A CASE expression doesn't control flow; it returns a single value. So something like this:

...
SET [DESC]=CASE [ATTDESC] 
  WHEN 'ABC' THEN PG.VAL + ' - ' + LD.DESC + ' - ' + GH.PL3NAME
  WHEN 'DEF' THEN PG.VAL + ' - ' + LD.DESC + ' - ' + GH.PL3NAME
  ELSE [DESC]
END
FROM 
...