Syntax:
ELT(N,str1,str2,str3,...)

ELT() returns the Nth element of the list of strings: str1 if N = 1,
str2 if N = 2, and so on. Returns NULL if N is less than 1 or greater
than the number of arguments. ELT() is the complement of FIELD().

URL: http://dev.mysql.com/doc/refman/5.7/en/string-functions.html

