Because the result of any arithmetic comparison with  NULL  is also  NULL , you cannot obtain any meaningful results from such comparisons. In MySQL,  0  or  NULL  means false and anything else means true. The default truth value from a boolean operation is  1 . This special treatment of  NULL  is why, in the previous section, it was necessary to determine which animals are no longer alive using  death IS NOT NULL  instead of  death <> NULL . Two  NULL  values are regarded as equal in a  GROUP BY . When doing an  ORDER BY ,  NULL  values are presented first if you do  ORDER BY ... ASC  and last if you do  ORDER BY ... DESC . A common error when working with  NULL  is to assume that it is not possible to insert a zero or an empty string into a column defined as  NOT NULL , but this is not the case. These are in fact values, whereas  NULL means “not having a value.”  You can test this easily enough by using  IS [NOT] NULL  as shown: Thus it is entirely possible to insert a zero or empty string into a  NOT NULL  column, as these are in fact NOT NULL . See Section B.3.4.3, “Problems with NULL Values” . MySQL provides standard SQL pattern matching as well as a form of pattern matching based on extended regular expressions similar to those used by Unix utilities such as  vi ,  grep , and  sed . SQL pattern matching enables you to use  _  to match any single character and  %  to match an arbitrary number of characters (including zero characters). In MySQL, SQL patterns are case-insensitive by default. Some examples are shown here. Do not use  =  or  <>  when you use SQL patterns. Use the  LIKE  or  NOT LIKE  comparison operators instead. To find names beginning with  b : To find names ending with  fy : Retrieving Information from a Table mysql>  SELECT 1 = NULL, 1 <> NULL, 1 < NULL, 1 > NULL; +----------+-----------+----------+----------+ | 1 = NULL | 1 <> NULL | 1 < NULL | 1 > NULL | +----------+-----------+----------+----------+ | NULL | NULL | NULL | NULL | +----------+-----------+----------+----------+ mysql>  SELECT 0 IS NULL, 0 IS NOT NULL, ’’ IS NULL, ’’ IS NOT NULL; +-----------+---------------+------------+----------------+ | 0 IS NULL | 0 IS NOT NULL | ’’ IS NULL | ’’ IS NOT NULL | +-----------+---------------+------------+----------------+ | 0 | 1 | 0 | 1 | +-----------+---------------+------------+----------------+ mysql>  SELECT * FROM pet WHERE name LIKE ’b%’; +--------+--------+---------+------+------------+------------+ | name | owner | species | sex | birth | death | +--------+--------+---------+------+------------+------------+ | Buffy | Harold | dog | f | 1989-05-13 | NULL | | Bowser | Diane | dog | m | 1989-08-31 | 1995-07-29 | +--------+--------+---------+------+------------+------------+ mysql>  SELECT * FROM pet WHERE name LIKE ’%fy’; +--------+--------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +--------+--------+---------+------+------------+-------+ 319 3.3.4.7 Pattern Matching