SQL
What NULL Really Means
NULL is not zero, not an empty string and not equal to itself. Learn what it represents, how it spreads through expressions and how to handle it delib...
NULL and Logic
What NULL means and how three valued logic changes every condition.
2 notes
Notes
SQL
Three Valued Logic: TRUE, FALSE and UNKNOWN
SQL conditions return three results, not two. Learn the AND, OR and NOT truth tables, why NOT IN breaks on NULL, and the NULL safe comparison operator...