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12.3.3 Logical Operators

Contents

Table 12.4 Logical Operators

Name Description
AND, && Logical AND
NOT, ! Negates value
OR, || Logical OR
XOR Logical XOR

In SQL, all logical operators evaluate to TRUE, FALSE, or NULL (UNKNOWN). In MySQL, these are implemented as 1 (TRUE), 0 (FALSE), and NULL. Most of this is common to different SQL database servers, although some servers may return any nonzero value for TRUE.

MySQL evaluates any nonzero, non-NULL value to TRUE. For example, the following statements all assess to TRUE:

  1. mysql> SELECT 10 IS TRUE;
  2. -> 1
  3. mysql> SELECT -10 IS TRUE;
  4. -> 1
  5. mysql> SELECT 'string' IS NOT NULL;
  6. -> 1

  • NOT, !

    Logical NOT. Evaluates to 1 if the operand is 0, to 0 if the operand is nonzero, and NOT NULL returns NULL.

    1. mysql> SELECT NOT 10;
    2.         -> 0
    3. mysql> SELECT NOT 0;
    4.         -> 1
    5. mysql> SELECT NOT NULL;
    6.         -> NULL
    7. mysql> SELECT ! (1+1);
    8.         -> 0
    9. mysql> SELECT ! 1+1;
    10.         -> 1

    The last example produces 1 because the expression evaluates the same way as (!1)+1.

    The !, operator is a nonstandard MySQL extension. As of MySQL 8.0.17, this operator is deprecated and support for it will be removed in a future MySQL version. Applications should be adjusted to use the standard SQL NOT operator.

  • AND, &&

    Logical AND. Evaluates to 1 if all operands are nonzero and not NULL, to 0 if one or more operands are 0, otherwise NULL is returned.

    1. mysql> SELECT 1 AND 1;
    2.         -> 1
    3. mysql> SELECT 1 AND 0;
    4.         -> 0
    5. mysql> SELECT 1 AND NULL;
    6.         -> NULL
    7. mysql> SELECT 0 AND NULL;
    8.         -> 0
    9. mysql> SELECT NULL AND 0;
    10.         -> 0

    The &&, operator is a nonstandard MySQL extension. As of MySQL 8.0.17, this operator is deprecated and support for it will be removed in a future MySQL version. Applications should be adjusted to use the standard SQL AND operator.

  • OR, ||

    Logical OR. When both operands are non-NULL, the result is 1 if any operand is nonzero, and 0 otherwise. With a NULL operand, the result is 1 if the other operand is nonzero, and NULL otherwise. If both operands are NULL, the result is NULL.

    1. mysql> SELECT 1 OR 1;
    2.         -> 1
    3. mysql> SELECT 1 OR 0;
    4.         -> 1
    5. mysql> SELECT 0 OR 0;
    6.         -> 0
    7. mysql> SELECT 0 OR NULL;
    8.         -> NULL
    9. mysql> SELECT 1 OR NULL;
    10.         -> 1
    Note

    If the PIPES_AS_CONCAT SQL mode is enabled, || signifies the SQL-standard string concatenation operator (like CONCAT()).

    The ||, operator is a nonstandard MySQL extension. As of MySQL 8.0.17, this operator is deprecated and support for it will be removed in a future MySQL version. Applications should be adjusted to use the standard SQL OR operator. Exception: Deprecation does not apply if PIPES_AS_CONCAT is enabled because, in that case, || signifies string concatentation.

  • XOR

    Logical XOR. Returns NULL if either operand is NULL. For non-NULL operands, evaluates to 1 if an odd number of operands is nonzero, otherwise 0 is returned.

    1. mysql> SELECT 1 XOR 1;
    2.         -> 0
    3. mysql> SELECT 1 XOR 0;
    4.         -> 1
    5. mysql> SELECT 1 XOR NULL;
    6.         -> NULL
    7. mysql> SELECT 1 XOR 1 XOR 1;
    8.         -> 1

    a XOR b is mathematically equal to (a AND (NOT b)) OR ((NOT a) and b).


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Document created the 26/06/2006, last modified the 26/10/2018
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