MySQL确实加入了MUL键的影响性能？

Question

我正在使用MySQL查询在四个表上执行三个表连接。其中两个连接在一对MUL键上。第三个连接是在一对主键上。查询需要一分钟才能抓取100行。

我相信两对MUL键都是唯一的;所以我想知道，如果这些密钥被索引为唯一密钥，或者是外键，我会注意到显着的性能提升吗？

MUL键上的连接可能是罪魁祸首吗？

修改

好的，这是架构。我用字母代替实际的表/列名称。

mysql> describe table A;
+-------------------+------------------+------+-----+---------+----------------+
| Field             | Type             | Null | Key | Default | Extra          |
+-------------------+------------------+------+-----+---------+----------------+
| pkey              | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| mkey              | int(10) unsigned | NO   | MUL | NULL    |                |
| a                 | int(10) unsigned | NO   |     | NULL    |                |
| b                 | int(10) unsigned | NO   |     | NULL    |                |

mysql> describe table B;
+-------------------+------------------+------+-----+---------+----------------+
| Field             | Type             | Null | Key | Default | Extra          |
+-------------------+------------------+------+-----+---------+----------------+
| pkey              | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| mkey1             | int(10) unsigned | NO   | MUL | NULL    |                |
| mkey2             | int(10) unsigned | NO   | MUL | NULL    |                |
| a                 | int(10) unsigned | NO   |     | NULL    |                |
| b                 | int(10) unsigned | NO   |     | NULL    |                |
| c                 | int(10) unsigned | NO   |     | NULL    |                |

mysql> describe table C;
+---------------+------------------+------+-----+---------+-------+
| Field         | Type             | Null | Key | Default | Extra |
+---------------+------------------+------+-----+---------+-------+
| pkey          | int(10) unsigned | NO   | PRI | NULL    |       |
| mkey          | varchar(128)     | NO   | MUL | NULL    |       |

mysql> describe table D;
+---------------+------------------+------+-----+---------+-------+
| Field         | Type             | Null | Key | Default | Extra |
+---------------+------------------+------+-----+---------+-------+
| pkey          | int(10) unsigned | NO   | PRI | NULL    |       |
| mkey          | varchar(128)     | NO   | MUL | NULL    |       |

查询：

select
A.a, A.b, B.c, A.mkey, C.pkey, D.mkey
from
A, B, C, D
where
A.pkey=C.pkey and
A.mkey=B.mkey1 and
B.mkey2=D.pkey and
B.a <= A.a and
B.b >= A.b
D.mkey in ('str1', 'str2', ...);

返回77行。

Answer 1

使用显式连接

select
A.a, A.b, B.c, A.mkey, C.pkey, D.mkey
from
A INNER JOIN C ON (A.pkey = C.pkey)
INNER JOIN B ON (A.mkey = B.mkey1)
INNER JOIN D ON (B.mkey2 = D.pkey)
where
B.a <= A.a and
B.b >= A.b
D.mkey in ('str1', 'str2', ...);