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MySQL 8.0 Reference Manual  /  ...  /  Logical Operators

12.3.3 Logical Operators

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:

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 AND 1;
            -> 1
    mysql> SELECT 1 AND 0;
            -> 0
    mysql> SELECT 1 AND NULL;
            -> NULL
    mysql> SELECT 0 AND NULL;
            -> 0
    mysql> SELECT NULL AND 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 OR 1;
            -> 1
    mysql> SELECT 1 OR 0;
            -> 1
    mysql> SELECT 0 OR 0;
            -> 0
    mysql> SELECT 0 OR NULL;
            -> NULL
    mysql> SELECT 1 OR 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).


User Comments
User comments in this section are, as the name implies, provided by MySQL users. The MySQL documentation team is not responsible for, nor do they endorse, any of the information provided here.
  Posted by Dredwerkz Dredwerkz on November 24, 2010
/*
* This is what I did to find out whether both AND, OR, &&, ||, &, | work as short circuit logical operators or not.
*
* Testing OR operand:
*/
SET @my_var := NULL;
SELECT IF(0 < 1 OR @my_var := (1 > 0), 'A', 'B') AS `rslt.`,
@my_var,
IF(0 > 1 OR @my_var := (1 > 0), 'A', 'B') AS `rslt.`,
@my_var;
/*
* The output:
* Query OK, 0 rows affected (0.00 sec)
*
* +-------+---------+-------+---------+
* | rslt. | @my_var | rslt. | @my_var |
* +-------+---------+-------+---------+
* | A | NULL | A | 1 |
* +-------+---------+-------+---------+
* 1 row in set (0.01 sec)
*
* Testing AND operand:
*/
SET @my_var := NULL;
SELECT IF(0 > 1 AND @my_var := (1 < 0), 'A', 'B') AS `rslt.`,
@my_var,
IF(0 < 1 AND @my_var := (1 < 0), 'A', 'B') AS `rslt.`,
@my_var;
/*
* The output:
* Query OK, 0 rows affected (0.00 sec)
*
* +-------+---------+-------+---------+
* | rslt. | @my_var | rslt. | @my_var |
* +-------+---------+-------+---------+
* | B | NULL | B | 0 |
* +-------+---------+-------+---------+
* 1 row in set (0.00 sec)
*
* Testing || operand:
*/
SET @my_var := NULL;
SELECT IF(0 < 1 || @my_var := (1 > 0), 'A', 'B') AS `rslt.`,
@my_var,
IF(0 > 1 || @my_var := (1 > 0), 'A', 'B') AS `rslt.`,
@my_var;
/*
* Query OK, 0 rows affected (0.00 sec)
*
* +-------+---------+-------+---------+
* | rslt. | @my_var | rslt. | @my_var |
* +-------+---------+-------+---------+
* | A | NULL | A | 1 |
* +-------+---------+-------+---------+
* 1 row in set (0.00 sec)
*
* Testing && operand:
*/
SET @my_var := NULL;
SELECT IF(0 > 1 AND @my_var := (1 < 0), 'A', 'B') AS `rslt.`,
@my_var,
IF(0 < 1 AND @my_var := (1 < 0), 'A', 'B') AS `rslt.`,
@my_var;
/*
* The output:
* Query OK, 0 rows affected (0.00 sec)
*
* +-------+---------+-------+---------+
* | rslt. | @my_var | rslt. | @my_var |
* +-------+---------+-------+---------+
* | B | NULL | B | 0 |
* +-------+---------+-------+---------+
* 1 row in set (0.00 sec)
*
* Testing the | operand:
*/
SET @my_var := NULL;
SELECT IF(0 < 1 | @my_var := (1 > 0), 'A', 'B') AS `rslt.`,
@my_var,
IF(0 > 1 | @my_var := (1 < 0), 'A', 'B') AS `rslt.`,
@my_var;
/*
* The output:
* Query OK, 0 rows affected (0.00 sec)
*
* +-------+---------+-------+---------+
* | rslt. | @my_var | rslt. | @my_var |
* +-------+---------+-------+---------+
* | A | 1 | B | 0 |
* +-------+---------+-------+---------+
* 1 row in set (0.00 sec)
*
* Testing the & operand:
*/
SET @my_var := NULL;
SELECT IF(0 > 1 & @my_var := (1 < 0), 'A', 'B') AS `rslt.`,
@my_var,
IF(0 < 1 | @my_var := (1 > 0), 'A', 'B') AS `rslt.`,
@my_var;
/*
* The output:
* Query OK, 0 rows affected (0.00 sec)
*
* +-------+---------+-------+---------+
* | rslt. | @my_var | rslt. | @my_var |
* +-------+---------+-------+---------+
* | B | 0 | A | 1 |
* +-------+---------+-------+---------+
* 1 row in set (0.01 sec)
*
*
* Summary:
* +---------+----------------+
* | Operand | Short-circuit? |
* +---------+----------------+
* | OR | Yes |
* +---------+----------------+
* | AND | Yes |
* +---------+----------------+
* | || | Yes |
* +---------+----------------+
* | && | Yes |
* +---------+----------------+
* | | | No |
* +---------+----------------+
* | & | No |
* +---------+----------------+
*/

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