Evaluate no result condition in SQL CASE

Question

I would like to use the SQL CASE keyword to evaluate the result of an inner query, in particular to check whether there is no record:

PseudoCode:

UPDATE tableA AS outerTable
SET field = CASE 
                WHEN (
                         SELECT * 
                         FROM tableB 
                         WHERE innerField = outerTable.field
                     ) IS [doesn't have result]
                THEN (
                        ...
                     ) 
                ELSE "default"
            END 

How can I code this condition? I've tried with IS NULL but it doesn't seem to work ( Scalar subquery produced more than one element)

Answer 1

You are looking for NOT EXISTS :

WHEN NOT EXISTS (SELECT * 
                 FROM tableB b
                 WHERE b.innerField = outerTable.field
                ) 
THEN . . .