(mysql.info.gz) Logical Operators

Info Catalog

(mysql.info.gz) Comparison Operators

(mysql.info.gz) Non-typed Operators

 
 12.1.4 Logical Operators
 ------------------------
 
 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 non-zero value for TRUE.
 
 `NOT'
 `!'
      Logical NOT.  Evaluates to `1' if the operand is `0', to `0' if
      the operand is non-zero, 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 non-zero 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
 
      Please note that MySQL versions prior to 4.0.5 stop evaluation when
      a `NULL' is encountered, rather than continuing the process to
      check for possible `0' values. This means that in these versions,
      `SELECT (NULL AND 0)' returns `NULL' instead of `0'.  As of MySQL
      4.0.5, the code has been re-engineered so that the result is
      always as prescribed by the SQL standards while still using the
      optimization wherever possible.
 
 `OR'
 `||'
      Logical OR.  When both operands are non-`NULL', the result is `1'
      if any operand is non-zero, and `0' otherwise.  With a `NULL'
      operand, the result is `1' if the other operand is non-zero, 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 non-zero, 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)'.
 
      `XOR' was added in MySQL 4.0.2.
 

Info Catalog

(mysql.info.gz) Comparison Operators

(mysql.info.gz) Non-typed Operators