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 . 第三个连接位于一对主键上 . 查询需要一分钟才能获得100行 .

我相信两对MUL键都是独一无二的;所以我想知道，如果这些密钥被索引为唯一的密钥，或者做成外键，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？

Edit

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 .