+-------+-------+---------------+------+---------+--------+--------+------------------------------------+
| table | type  | possible_keys | key  | key_len | ref    | rows   | Extra                              |
+-------+-------+---------------+------+---------+--------+--------+------------------------------------+
| c     | index | SIC           | SIC  |       6 | NULL   | 283437 | Using index; Using temporary       |
| l     | ref   | SIC           | SIC  |       2 | c.sic1 |    137 | Using where; Using index; Distinct |
+-------+-------+---------------+------+---------+--------+--------+------------------------------------+