分析sql及表结构如下
MySQL > EXPLAIN SELECT COUNT(UA.id) AS tp_count FROM ck_user_audit UA RIGHT JOIN ck_user AS U ON U.id = UA.uid LIMIT 1;
+----+-------------+-------+------------+-------+---------------+------+---------+------+-------+----------+----------------------------------------------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+-------+------------+-------+---------------+------+---------+------+-------+----------+----------------------------------------------------+
*| 1 | SIMPLE | U | NULL | index | NULL | pid | 5 | NULL | 23003 | 100.00 | Using index |
| 1 | SIMPLE | UA | NULL | ALL | NULL | NULL | NULL | NULL | 3304 | 100.00 | Using where; Using join buffer (Block Nested Loop) |
+----+-------------+-------+------------+-------+---------------+------+---------+------+-------+----------+----------------------------------------------------+
MySQL > desc ck_user;
+-----------------+---------------------+------+-----+------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------------+---------------------+------+-----+------------+----------------+
| id | int(10) | NO | PRI | NULL | auto_increment |
| phone | char(50) | YES | MUL | NULL | |
| pid | int(10) | YES | MUL | NULL | |
| email | char(100) | YES | MUL | NULL | |
执行sql用的是id这个主键，为什么分析出来却显示用的是pid这个索引？
