Syntax:
expr IN (value,...)

Returns 1 if expr is equal to any of the values in the IN list, else
returns 0. If all values are constants, they are evaluated according to
the type of expr and sorted. The search for the item then is done using
a binary search. This means IN is very quick if the IN value list
consists entirely of constants. Otherwise, type conversion takes place
according to the rules described in
http://dev.mysql.com/doc/refman/5.1/en/type-conversion.html, but
applied to all the arguments.

URL: http://dev.mysql.com/doc/refman/5.1/en/comparison-operators.html

