NULL and Predicates: Three-Valued Logic, LIKE, IN, BETWEEN and COALESCE
In SQL a comparison has three outcomes: TRUE, FALSE and UNKNOWN; that is why = NULL finds no rows, NOT on a nullable column also drops the NULL rows, and a single NULL in a NOT IN list empties the result. We show the type difference between COALESCE and ISNULL, guarding division by zero with NULLIF, escaping in LIKE and how a leading % affects the index, and how BETWEEN misses the last day of a date range, with real output.
8 Nov 2026
·
14 min
·
4
