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mysql> EXPLAIN EXTENDED SELECT * FROM styles s, customers c where s.customers_id = c.customers_id group by s.styles_id;
+----+-------------+-------+--------+---------------+---------+---------+-----------------------------+-------+----------+---------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+-------+--------+---------------+---------+---------+-----------------------------+-------+----------+---------------------------------+
| 1 | SIMPLE | s | ALL | customers_id | NULL | NULL | NULL | 41946 | 100.00 | Using temporary; Using filesort |
| 1 | SIMPLE | c | eq_ref | PRIMARY | PRIMARY | 4 | revgrp_admin.s.customers_id | 1 | 100.00 | |
+----+-------------+-------+--------+---------------+---------+---------+-----------------------------+-------+----------+---------------------------------+
2 rows in set, 1 warning (0.00 sec)