MySQL忽略了我的索引

Question

我在MYSQL中运行以下查询

select distinct straight_join
   cu.entryid entryid,
   t0.tokpos starting_position,
   t3.tokpos ending_position,
   t0.idxsent idxsent,
   'TOKENS_44_340' tablename
from
   TOKENS_44_340 t0,
   constraints_appraisal cu,
   TOKENS_44_340 t1,
   TOKENS_44_340 t2,
   TOKENS_44_340 t3
where
t0.token_surface = cu.token_0
and (cu.pos_0 is null OR t0.penntag like concat(cu.pos_0,'%'))
and t1.token_surface = cu.token_1
and (cu.pos_1 is null OR t1.penntag like concat(cu.pos_1,'%'))
and t2.token_surface = cu.token_2
and (cu.pos_2 is null OR t2.penntag like concat(cu.pos_2,'%'))
and t3.token_surface = cu.token_3
and (cu.pos_3 is null OR t3.penntag like concat(cu.pos_3,'%'))
and t0.tokpos = t1.tokpos - 1
and t1.tokpos = t2.tokpos - 1
and t2.tokpos = t3.tokpos - 1
and cu.token_4 is null
and cu.token_5 is null
and cu.token_6 is null
and cu.token_7 is null
and cu.token_8 is null
and cu.token_9 is null;

MySQL为此查询提供了以下查询计划：

+----+-------------+-------+------+---------------------------------------+------------------------+---------+------+------+-----------------+
| id | select_type | table | type | possible_keys                         | key                    | key_len | ref  | rows | Extra           |
+----+-------------+-------+------+---------------------------------------+------------------------+---------+------+------+-----------------+
|  1 | SIMPLE      | t0    | ALL  | PRIMARY,TOKENS_44_340_index_44,tokpos | NULL                   | NULL    | NULL |   49 | Using temporary | 
|  1 | SIMPLE      | cu    | ALL  | NULL                                  | NULL                   | NULL    | NULL | 7907 | Using where     | 
|  1 | SIMPLE      | t1    | ref  | PRIMARY,TOKENS_44_340_index_44,tokpos | TOKENS_44_340_index_44 | 399     | func |    4 | Using where     | 
|  1 | SIMPLE      | t2    | ref  | PRIMARY,TOKENS_44_340_index_44,tokpos | TOKENS_44_340_index_44 | 399     | func |    4 | Using where     | 
|  1 | SIMPLE      | t3    | ref  | TOKENS_44_340_index_44                | TOKENS_44_340_index_44 | 399     | func |    4 | Using where     | 
+----+-------------+-------+------+---------------------------------------+------------------------+---------+------+------+-----------------+
5 rows in set (0.00 sec)

正如您所看到的，MySQL甚至没有承认token_0上我的索引constraints_appraisal(token_0)的存在。知道为什么它忽略了我的索引，我能做些什么呢？我正在为Debian stable运行mysql 5.0.51a-24 + lenny4。

P.S。我知道我可以通过删除straight_join约束并让它使用token_surface index t0来更快地运行此查询，但它仍然不会像使用token_0那样快constraints_appraisal上的straight_join索引。我添加了mysql> describe TOKENS_44_340; +---------------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------------+--------------+------+-----+---------+-------+ | tokPos | int(11) | NO | PRI | NULL | | | linePos | int(11) | YES | | NULL | | | EOLs | int(11) | YES | | NULL | | | idxsent | int(11) | YES | | NULL | | | possent | int(11) | YES | | NULL | | | brilltag | int(11) | YES | | NULL | | | token_surface | varchar(132) | YES | MUL | NULL | | | wordLen | int(11) | YES | | NULL | | | capitalized | int(11) | YES | | NULL | | | wordType | int(11) | YES | | NULL | | | numDigit | int(11) | YES | | NULL | | | numPunc | int(11) | YES | | NULL | | | numAlpha | int(11) | YES | | NULL | | | maxRep | int(11) | YES | | NULL | | | pre1 | varchar(132) | YES | | NULL | | | pre2 | varchar(132) | YES | | NULL | | | pre3 | varchar(132) | YES | | NULL | | | pre4 | varchar(132) | YES | | NULL | | | suf1 | varchar(132) | YES | | NULL | | | suf2 | varchar(132) | YES | | NULL | | | suf3 | varchar(132) | YES | | NULL | | | suf4 | varchar(132) | YES | | NULL | | | dep_gov | int(11) | YES | MUL | NULL | | | dep_rel | varchar(20) | YES | MUL | NULL | | | penntag | varchar(30) | YES | | NULL | | +---------------+--------------+------+-----+---------+-------+ 25 rows in set (0.04 sec) mysql> describe constraints_appraisal; +---------------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------------+--------------+------+-----+---------+-------+ | entryid | int(11) | NO | PRI | 0 | | | context | varchar(50) | YES | | NULL | | | syntax | int(11) | YES | | NULL | | | token_0 | varchar(50) | YES | MUL | NULL | | | pos_0 | varchar(50) | YES | | NULL | | | porter_0 | varchar(50) | YES | MUL | NULL | | | token_1 | varchar(50) | YES | | NULL | | | pos_1 | varchar(50) | YES | | NULL | | | porter_1 | varchar(50) | YES | | NULL | | | token_2 | varchar(50) | YES | | NULL | | | pos_2 | varchar(50) | YES | | NULL | | | porter_2 | varchar(50) | YES | | NULL | | | token_3 | varchar(50) | YES | | NULL | | | pos_3 | varchar(50) | YES | | NULL | | | porter_3 | varchar(50) | YES | | NULL | | | token_4 | varchar(50) | YES | | NULL | | | pos_4 | varchar(50) | YES | | NULL | | | porter_4 | varchar(50) | YES | | NULL | | | token_5 | varchar(50) | YES | | NULL | | | pos_5 | varchar(50) | YES | | NULL | | | porter_5 | varchar(50) | YES | | NULL | | | token_6 | varchar(50) | YES | | NULL | | | pos_6 | varchar(50) | YES | | NULL | | | porter_6 | varchar(50) | YES | | NULL | | | token_7 | varchar(50) | YES | | NULL | | | pos_7 | varchar(50) | YES | | NULL | | | porter_7 | varchar(50) | YES | | NULL | | | token_8 | varchar(50) | YES | | NULL | | | pos_8 | varchar(50) | YES | | NULL | | | porter_8 | varchar(50) | YES | | NULL | | | token_9 | varchar(50) | YES | | NULL | | | pos_9 | varchar(50) | YES | | NULL | | | porter_9 | varchar(50) | YES | | NULL | | | token_surface | varchar(200) | YES | | NULL | | | fileid | varchar(100) | YES | | NULL | | +---------------+--------------+------+-----+---------+-------+ 35 rows in set (0.06 sec) mysql> show index from constraints_appraisal; +-----------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | +-----------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ | constraints_appraisal | 0 | PRIMARY | 1 | entryid | A | 7907 | NULL | NULL | | BTREE | | | constraints_appraisal | 1 | token_0 | 1 | token_0 | A | NULL | NULL | NULL | YES | BTREE | | | constraints_appraisal | 1 | porter_0 | 1 | porter_0 | A | NULL | NULL | NULL | YES | BTREE | | +-----------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ 3 rows in set (0.05 sec) ，以便我可以更清楚地显示我的具体问题，并且我计划在索引正常工作时删除它。

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Answer 1

看来问题是这两个表是不同的字符集。

• TOKENS_44_340位于utf8
• constraints_appraisal位于latin1