Returns NULL if N is less than 1 or greater than the number of arguments.
ELT() is the complement of FIELD().
mysql>
mysql> SELECT ELT(1, 'A', 'B', 'C', 'D');
+----------------------------+
| ELT(1, 'A', 'B', 'C', 'D') |
+----------------------------+
| A |
+----------------------------+
1 row in set (0.00 sec)
mysql>