11.3.3. Logical Operators

Table 11.4. Logical Operators

NameDescription
AND, &&Logical AND
NOT, !Negates value
||, ORLogical OR
XORLogical 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:

mysql> SELECT 10 IS TRUE;
-> 1
mysql> SELECT -10 IS TRUE;
-> 1
mysql> SELECT 'string' IS NOT NULL;
-> 1
  • NOT, !

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

    mysql> SELECT NOT 10;
            -> 0
    mysql> SELECT NOT 0;
            -> 1
    mysql> SELECT NOT NULL;
            -> NULL
    mysql> SELECT ! (1+1);
            -> 0
    mysql> SELECT ! 1+1;
            -> 1
    

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

  • 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.

    mysql> SELECT 1 && 1;
            -> 1
    mysql> SELECT 1 && 0;
            -> 0
    mysql> SELECT 1 && NULL;
            -> NULL
    mysql> SELECT 0 && NULL;
            -> 0
    mysql> SELECT NULL && 0;
            -> 0
    
  • 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.

    mysql> SELECT 1 || 1;
            -> 1
    mysql> SELECT 1 || 0;
            -> 1
    mysql> SELECT 0 || 0;
            -> 0
    mysql> SELECT 0 || NULL;
            -> NULL
    mysql> SELECT 1 || NULL;
            -> 1
    
  • 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.

    mysql> SELECT 1 XOR 1;
            -> 0
    mysql> SELECT 1 XOR 0;
            -> 1
    mysql> SELECT 1 XOR NULL;
            -> NULL
    mysql> SELECT 1 XOR 1 XOR 1;
            -> 1
    

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

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