NULL-aware inequality: what gets filtered out?

Question

Accepted Answer

IS DISTINCT FROM returns TRUE when two values are different, with full NULL awareness. Two NULLs are NOT distinct from each other (same as IS NOT DISTINCT FROM in reverse), so the NULL | NULL row is excluded. A NULL and a non-NULL are always distinct, so NULL | 5 is included. Compare this to `x <> y` which would return UNKNOWN for any row involving NULL.