# Logical Operators

The usual logical operators are available for boolean values:
`AND`

, `OR`

, `NOT`

.
SQL uses a three-valued logic system with true, false, and `null`

,
which represents "unknown". Observe the following truth tables:

`a` | `b` | `a AND b` | `a OR b` |
---|---|---|---|

TRUE | TRUE | TRUE | TRUE |

TRUE | FALSE | FALSE | TRUE |

TRUE | NULL | NULL | TRUE |

FALSE | FALSE | FALSE | FALSE |

FALSE | NULL | FALSE | NULL |

NULL | NULL | NULL | NULL |

`a` | `NOT a` |
---|---|

TRUE | FALSE |

FALSE | TRUE |

NULL | NULL |

The operators `AND`

and `OR`

are commutative, that is, you can switch
the left and right operand without affecting the result.