Logical Operators -> 1 ISNULL()  can be used instead of  =  to test whether a value is  NULL . (Comparing a value to  NULL  using =  always yields  NULL .) The  ISNULL()  function shares some special behaviors with the  IS NULL  comparison operator. See the description of  IS NULL . With two or more arguments, returns the smallest (minimum-valued) argument. The arguments are compared using the following rules: • LEAST( value1 , value2 ,...) •If any argument is  NULL , the result is  NULL . No comparison is needed. •If all arguments are integer-valued, they are compared as integers. •If at least one argument is double precision, they are compared as double-precision values. Otherwise, if at least one argument is a  DECIMAL  value, they are compared as  DECIMAL  values. •If the arguments comprise a mix of numbers and strings, they are compared as strings. •If any argument is a nonbinary (character) string, the arguments are compared as nonbinary strings. •In all other cases, the arguments are compared as binary strings. The return type of  LEAST()  is the aggregated type of the comparison argument types. mysql>  SELECT LEAST(2,0); -> 0 mysql>  SELECT LEAST(34.0,3.0,5.0,767.0); -> 3.0 mysql>  SELECT LEAST(’B’,’A’,’C’); -> ’A’ 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 Table 12.5 Logical Operators 12.4.3 Logical Operators Name Description AND ,  && Logical AND NOT ,  ! Negates value OR ,  || Logical OR XOR Logical XOR 2131