mysql 外键和索引

Question

如果我有两张 table

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

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

现在，如果 user.id <-> adress.user_id 之间存在一对多外键是否还需要在 user_id 列中创建索引以加速选择查询？

或者因为我创建了外键，所以我还隐式创建了一个索引，该索引将从 dmbs 中使用来加速查询？

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 ...