# Pastebin MftvYe3g
MySQL [nova_api]> EXPLAIN SELECT DISTINCT instance_mappings.cell_id FROM instance_mappings WHERE instance_mappings.project_id = '86bbbcfa8ad043109d2d7af530225c72';
+----+-------------+-------------------+------------+------+------------------------+----------------+---------+-------+---------+----------+----------------------------------------+
| id | select_type | table             | partitions | type | possible_keys          | key            | key_len | ref   | rows    | filtered | Extra                                  |
+----+-------------+-------------------+------------+------+------------------------+----------------+---------+-------+---------+----------+----------------------------------------+
|  1 | SIMPLE      | instance_mappings | NULL       | ref  | cell_id,project_id_idx | project_id_idx | 767     | const | 1262660 |   100.00 | Using index condition; Using temporary |
+----+-------------+-------------------+------------+------+------------------------+----------------+---------+-------+---------+----------+----------------------------------------+