IS [ NOT ]

Compares whether two expressions are equal (or not equal). The function is NULL-safe, meaning it treats NULLs as known values for comparing equality. Note that this is different from the EQUAL comparison operator (=), which treats NULLs as unknown values.

Syntax

<expr1> IS [ NOT ] <expr2>

Returns

The value returned depends on whether any of the inputs are NULL values:

• Returns TRUE, if:
  • <null> IS NOT <null>
  • <null> IS <not_null>
  • <not_null> IS <null>
• Returns FALSE, if:
  • <null> IS <null>
  • <null> IS NOT <not_null>
  • <not_null> IS NOT <null>
• Otherwise,
  • <expr1> IS <expr2> is equivalent to <expr1> != <expr2>
  • <expr1> IS NOT <expr2> is equivalent to <expr1> = <expr2>