   FIND_IN_SET(str,strlist)
Returns a value 1 to N if the string str is in the string list
strlist consisting of N substrings. A string list is a string
composed of substrings separated by ',' characters. If the first
argument is a constant string and the second is a column of type SET,
the FIND_IN_SET() function is optimized to use bit arithmetic.
Returns 0 if str is not in strlist or if strlist
is the empty string.  Returns NULL if either argument is NULL.
This function does not work properly if the first argument contains a comma
(',') character.
