Mysql 5.1.49 InnoDB /查询优化器动作怪异？

Question

我有以下InnoDB表，其作用MySQL的49年5月1日 下有点奇怪（MySQL的版本14.14 DISTRIB 49年5月1日，使用readline的6.1 Debian的Linux-GNU（x86_64的））

mysql> desc forum_favorite; 
+-----------+----------------------+------+-----+---------+-------+ 
| Field  | Type     | Null | Key | Default | Extra | 
+-----------+----------------------+------+-----+---------+-------+ 
| id_member | smallint(5) unsigned | YES | MUL | NULL |  | 
| id_topic | int(10) unsigned  | YES | MUL | NULL |  | 
+-----------+----------------------+------+-----+---------+-------+ 
2 rows in set (0.00 sec) 

mysql> show index from forum_favorite; 
+----------------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ 
| Table   | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | 
+----------------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ 
| forum_favorite |   1 | id_member |   1 | id_member | A   |  2134 |  NULL | NULL | YES | BTREE  |   | 
| forum_favorite |   1 | id_topic |   1 | id_topic | A   |  3201 |  NULL | NULL | YES | BTREE  |   | 
+----------------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ 
2 rows in set (0.00 sec) 

现在，检查查询：

mysql> SELECT id_topic FROM forum_favorite WHERE (id_member = 2); 
+----------+ 
| id_topic | 
+----------+ 
|  1249 | 
| 20209 | 
| 91878 | 
| 99026 | 
| 90257 | 
|  1179 | 
|  1179 | 
+----------+ 
7 rows in set (0.00 sec) 

当我搜索与给定成员一个特定的主题，它提供了一个空的结果集。为什么？

mysql> select * from forum_favorite where id_member = 2 and id_topic = 1249; 
Empty set (0.00 sec) 

但是，当我寻找另一个话题，它回来确定...

可以毫不id_member where子句中找到：

mysql> select * from forum_favorite where id_topic = 1249; 
+-----------+----------+ 
| id_member | id_topic | 
+-----------+----------+ 
|   2 |  1249 | 
+-----------+----------+ 
1 rows in set (0.00 sec) 

指标：

mysql> show index from forum_favorite; 
+----------------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ 
| Table   | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | 
+----------------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ 
| forum_favorite |   1 | id_member |   1 | id_member | A   |  2134 |  NULL | NULL | YES | BTREE  |   | 
| forum_favorite |   1 | id_topic |   1 | id_topic | A   |  3201 |  NULL | NULL | YES | BTREE  |   | 
+----------------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ 
2 rows in set (0.00 sec) 

解释犯罪查询：

mysql> explain select * from forum_favorite where id_member = 2 and id_topic = 1249; 
+----+-------------+----------------+-------------+--------------------+--------------------+---------+------+------+---------------------------------------------------------------+ 
| id | select_type | table   | type  | possible_keys  | key    | key_len | ref | rows | Extra               | 
+----+-------------+----------------+-------------+--------------------+--------------------+---------+------+------+---------------------------------------------------------------+ 
| 1 | SIMPLE  | forum_favorite | index_merge | id_member,id_topic | id_member,id_topic | 3,5  | NULL | 1 | Using intersect(id_member,id_topic); Using where; Using index | 
+----+-------------+----------------+-------------+--------------------+--------------------+---------+------+------+---------------------------------------------------------------+ 
1 row in set (0.00 sec) 

用另一个topicid解释查询。搞什么鬼？？？

mysql> explain select * from forum_favorite where (id_member = 2) and id_topic = 20209; 
+----+-------------+----------------+------+--------------------+----------+---------+-------+------+-------------+ 
| id | select_type | table   | type | possible_keys  | key  | key_len | ref | rows | Extra  | 
+----+-------------+----------------+------+--------------------+----------+---------+-------+------+-------------+ 
| 1 | SIMPLE  | forum_favorite | ref | id_member,id_topic | id_topic | 5  | const | 1 | Using where | 
+----+-------------+----------------+------+--------------------+----------+---------+-------+------+-------------+ 
1 row in set (0.00 sec 

我已经从旧的mysql 4.x数据库迁移到mysql 5.1最近，上述查询给出一致的结果。 可能是什么问题？！？！是什么让优化器变成疯子？

Answer 1

您是否试过在桌上运行OPTIMIZE？

UPD：

对于InnoDB表，OPTIMIZE TABLE被映射到ALTER TABLE，以重新生成表更新聚集索引指数统计和自由未使用的空间。

我觉得问题其实是在Using intersect(id_member,id_topic);。我会将id_topic索引扩展到（id_topic，id_member），以便它使用单个键进行查找，而不是索引合并（在MySQL中实际上很少见）。