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    1. General Information
    2. MySQL Installation
    3. Tutorial Introduction
    4. Database Administration
    5. MySQL Optimisation
    6. MySQL Language Reference
    7. MySQL Table Types
    8. MySQL APIs
    9. Extending MySQL
    Chapter 6:  MySQL Language Reference 411 6.3.1.3  Logical Operators All logical operators evaluate to 1 (TRUE), 0 (FALSE) or NULL (unknown, which is in most cases the same as FALSE): NOT ! Logical  NOT.  Evaluates  to  1  if  the  operand  is  0,  otherwise  evaluates  to  0. Exception:  NOT NULL evaluates to NULL: mysql> SELECT NOT 1; -> 0 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. OR || Logical OR. Evaluates to 1 if either operand is not 0 and not NULL: mysql> SELECT 1 || 0; -> 1 mysql> SELECT 0 || 0; -> 0 mysql> SELECT 1 || NULL; -> 1 AND && Logical AND. For non-NULL operands, evaluates to 1 if both operands are non- zero and to 0 otherwise.  Produces NULL if either operand is NULL: mysql> SELECT 1 && 1; -> 1 mysql> SELECT 1 && 0; -> 0 mysql> SELECT 1 && NULL; -> NULL XOR Logical XOR. For non-NULL operands, evaluates to 1 if only one of the operators is non-zero.  Produces NULL if either operand is NULL: mysql> SELECT 1 XOR 1; -> 0 mysql> SELECT 1 XOR 0; -> 1 mysql> SELECT 1 XOR NULL; -> NULL a XOR b is equal to (a AND (NOT b)) OR ((NOT a) and b).
     

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