Question

I was wondering if the where condition in a select statement has a nullable variable. Does it have to use a IF condition to write the same select statement twice like below? Is there a better way?

FUNCTION function1(
    foo   IN  INTEGER,
  ) RETURN INTEGER
    ret      INTEGER;
  BEGIN

IF foo IS NULL THEN
  SELECT COUNT(*) INTO ret FROM t WHERE t.col IS NULL;
ELSE
  SELECT COUNT(*) INTO ret FROM t WHERE t.col = foo;
END IF;
RETURN ret;

END function1;

Answer 1

You can always do

SELECT COUNT(*) 
  INTO ret 
  FROM t 
 WHERE (t.col IS NULL AND foo IS NULL)
    OR t.col = foo;

That can be simplified to

SELECT COUNT(*) 
  INTO ret 
  FROM t 
 WHERE NVL(t.col, 'Some Impossible Value') = NVL(foo, 'Some Impossible Value');

though you may need a function-based index on NVL(t.col, 'Some Impossible Value') to make the query performant.