Consider the case of the current /notifications filter condition:
WHERE ... NOT ((comments.sentto = 2) AND (users.is_muted))
SELECT 1 WHERE NOT ((null = 2) AND (true)); ⇒ 0 rows
SELECT 1 WHERE NOT ((1 = 2) AND (true)); ⇒ 1 row
SELECT 1 WHERE NOT ((2 = 2) AND (true)); ⇒ 0 rows
We want the first expression, where comments.sentto = null, to evaluate
to false, not to null, so it negates to true. Behavior as written is:
SELECT 1 WHERE NOT ((null = 2) AND (true)); →
SELECT 1 WHERE NOT (null AND true); →
SELECT 1 WHERE NOT null; →
SELECT 1 WHERE null;
Which guarantees a null return set. If we check first for non-nullity:
SELECT 1 WHERE NOT ((null IS NOT null) AND (null = 2) AND (true)); ⇒ 1
SELECT 1 WHERE NOT ((1 IS NOT null) AND (1 = 2) AND (true)); ⇒ 1
SELECT 1 WHERE NOT ((2 IS NOT null) AND (2 = 2) AND (true)); ⇒ 0
Snakes
9eab252e5b
