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IS TRUE, IS FALSE, IS UNKNOWN Predicates

The IS Boolean operator behaves according to the following truth table:

IS | TRUE | FALSE | UNKNOWN |

True | True | False | False |

False | False | True | False |

Unknown | False | False | True |

That is:

• IS TRUE is true for a BOOLEAN TRUE.

• IS FALSE is true for a BOOLEAN FALSE.

• IS UNKNOWN is true for an unknown (NULL) value.

• Every other comparison is false.

When applied to row value expressions, all elements must test the same.