expression1  IS [ NOT ] DISTINCT FROM expression2 

The IS DISTINCT FROM and IS NOT DISTINCT FROM search conditions are sargable and evaluate to TRUE or FALSE.

The IS NOT DISTINCT FROM search condition evaluates to TRUE if expression1 is equal to expression2, or if both expressions are NULL. This is equivalent to a combination of two search conditions, as follows:

expression1 = expression2 OR ( expression1 IS NULL AND expression2 IS NULL )

The IS DISTINCT FROM syntax reverses the meaning. That is, IS DISTINCT FROM evaluates to TRUE if expression1 is not equal to expression2, and at least one of the expressions is not NULL. This is equivalent to the following:

NOT( expression1 = expression2 OR ( expression1 IS NULL AND expression2 IS NULL ))

• Query predicates