MySQL :: MySQL 8.0 Reference Manual :: 12.3.3 Logical Operators

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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).

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User Comments

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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 |
* +---------+----------------+
*/