mysql> explain SELECT prefix02,suffix,chain_ID,prefix01,start FROM chain WHERE prefix01=44 order by rand() LIMIT 1;
+----+-------------+-------+------------+------+----------------+----------------+---------+-------+---------+----------+---------------------------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+-------+------------+------+----------------+----------------+---------+-------+---------+----------+---------------------------------+
| 1 | SIMPLE | chain | NULL | ref | INDEX_PREFIX01 | INDEX_PREFIX01 | 9 | const | 1986170 | 100.00 | Using temporary; Using filesort |
+----+-------------+-------+------------+------+----------------+----------------+---------+-------+---------+----------+---------------------------------+
