mysql 外键和索引

Question

如果我有2张桌子

user
-----------------
id integer PK
name varchar

address
----------------
id integer PK
user_id integer
city varchar

现在，如果 user.id <-> adress.user_id 之间存在一对多的外键还需要在 user_id 列中创建索引以加速 select 查询？

或者因为我已经创建了一个外键，所以我还隐式创建了一个索引，该索引将从 dmbs 中用于加速查询？

Answer 1

索引为created automatically when creating an FK:

The index_name value is ignored if there is already an explicitly defined index on the child table that can support the foreign key. Otherwise, MySQL implicitly creates a foreign key index that is named according to the following rules ...

Answer 2

查看这篇文章：http://dev.mysql.com/doc/refman/5.0/en/innodb-foreign-key-constraints.html

InnoDB permits a foreign key to reference any index column or group of columns. However, in the referenced table, there must be an index where the referenced columns are listed as the first columns in the same order.

所以上面有一个索引 table

mysql 外键和索引

mysql foreign keys and indexs

mysql

innodb