Returns 0 if str is not found.
If str is NULL, the return value is 0.
FIELD() is the complement of ELT().
mysql>
mysql> SELECT FIELD('A', 'B', 'A', 'V', 'D', 'W');
+-------------------------------------+
| FIELD('A', 'B', 'A', 'V', 'D', 'W') |
+-------------------------------------+
| 2 |
+-------------------------------------+
1 row in set (0.00 sec)
mysql>
mysql> SELECT FIELD('Z', 'A', 'B', 'C', 'D', 'E');
+-------------------------------------+
| FIELD('Z', 'A', 'B', 'C', 'D', 'E') |
+-------------------------------------+
| 0 |
+-------------------------------------+
1 row in set (0.02 sec)
mysql>