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我試圖跑在我的數據庫以下查詢特定索引：不是MySQL使用
SELECT * FROM ts_cards WHERE (cardstatus= 2 OR cardstatus= 3) AND (cardtype= 1 OR cardtype= 2) ORDER BY cardserial DESC LIMIT 10;
所有三個字段（cardstatus，cardtype和cardserial）被編入索引：
mysql> SHOW INDEX FROM ts_cards;
+----------+------------+----------------+--------------+-------------------+-----------+-------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+----------+------------+----------------+--------------+-------------------+-----------+-------------+----------+--------+------+------------+---------+
| ts_cards | 0 | PRIMARY | 1 | card_id | A | 15000134 | NULL | NULL | | BTREE | |
| ts_cards | 1 | CardID | 1 | cardserial | A | 15000134 | NULL | NULL | | BTREE | |
| ts_cards | 1 | CardType | 1 | cardtype | A | 17 | NULL | NULL | | BTREE | |
| ts_cards | 1 | CardHolder | 1 | cardstatusholder | A | 17 | NULL | NULL | | BTREE | |
| ts_cards | 1 | CardExpiration | 1 | cardexpiredstatus | A | 17 | NULL | NULL | | BTREE | |
| ts_cards | 1 | CardStatus | 1 | cardstatus | A | 17 | NULL | NULL | | BTREE | |
+----------+------------+----------------+--------------+-------------------+-----------+-------------+----------+--------+------+------------+---------+
6 rows in set (0.22 sec)
（是的，我知道索引的名字吸）
但是，默認情況下，MySQL只使用cardstatus的索引：
mysql> EXPLAIN SELECT * FROM `ts_cards` WHERE (cardstatus= 2 OR cardstatus= 3) AND (cardtype= 1 OR cardtype= 2) ORDER BY cardserial DESC LIMIT 10;
+----+-------------+----------+-------+---------------------+------------+---------+------+---------+-----------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+----------+-------+---------------------+------------+---------+------+---------+-----------------------------+
| 1 | SIMPLE | ts_cards | range | CardType,CardStatus | CardStatus | 1 | NULL | 3215967 | Using where; Using filesort |
+----+-------------+----------+-------+---------------------+------------+---------+------+---------+-----------------------------+
1 row in set (0.00 sec)
（它甚至不考慮cardserial的索引，但我想這是另外一個問題。）
使用「USE KEY」或「力鑰匙」可以使其使用cardtype的指數，但不能同時cardtype和cardstatus：
mysql> EXPLAIN SELECT * FROM `ts_cards` FORCE KEY (CardType) WHERE (cardstatus= 2 OR cardstatus= 3) AND (cardtype= 1 OR cardtype= 2) ORDER BY cardserial DESC LIMIT 10;
+----+-------------+----------+-------+---------------+----------+---------+------+---------+-----------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+----------+-------+---------------+----------+---------+------+---------+-----------------------------+
| 1 | SIMPLE | ts_cards | range | CardType | CardType | 1 | NULL | 6084861 | Using where; Using filesort |
+----+-------------+----------+-------+---------------+----------+---------+------+---------+-----------------------------+
1 row in set (0.00 sec)
mysql> EXPLAIN SELECT * FROM `ts_cards` FORCE KEY (CardType,CardStatus) WHERE (cardstatus= 2 OR cardstatus= 3) AND (cardtype= 1 OR cardtype= 2) ORDER BY cardserial DESC LIMIT 10;
+----+-------------+----------+-------+---------------------+------------+---------+------+---------+-----------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+----------+-------+---------------------+------------+---------+------+---------+-----------------------------+
| 1 | SIMPLE | ts_cards | range | CardType,CardStatus | CardStatus | 1 | NULL | 3215967 | Using where; Using filesort |
+----+-------------+----------+-------+---------------------+------------+---------+------+---------+-----------------------------+
1 row in set (0.00 sec)
如何強制MySQL使用兩個索引來加快查詢？ cardtype和cardstatus索引似乎都以相同的方式定義，但cardstatus似乎優先於cardtype。