Standard SQL boolean operator IS vs. equals (=) operator

Question

On the Wikipedia page for SQL there are some truth tables about boolean logic in SQL. [1] The Wikipedia page seems to source the SQL:2003 standard.

The truth table f

Answer 1

That's a new one for me.

If I read that correctly the grammar defines three predicates solely for use with the boolean datatype IS TRUE, IS FALSE, IS UNKNOWN.

These differ from their equality counterparts in that they only evaluate to True or False. Never to Unknown. i.e. UNKNOWN = TRUE would evaluate to UNKNOWN but UNKNOWN IS TRUE evaluates to False.

The full truth tables for IS and = are below.

+---------+-------+-------+---------+
|   IS    | TRUE  | FALSE | UNKNOWN |
+---------+-------+-------+---------+
| TRUE    | TRUE  | FALSE | FALSE   |
| FALSE   | FALSE | TRUE  | FALSE   |
| UNKNOWN | FALSE | FALSE | TRUE    |
+---------+-------+-------+---------+

As opposed to

+---------+---------+---------+---------+
|    =    |  TRUE   |  FALSE  | UNKNOWN |
+---------+---------+---------+---------+
| TRUE    | TRUE    | FALSE   | UNKNOWN |
| FALSE   | FALSE   | TRUE    | UNKNOWN |
| UNKNOWN | UNKNOWN | UNKNOWN | UNKNOWN |
+---------+---------+---------+---------+