我正在从多个表执行 JOIN 以执行分面搜索。当避免 JOIN 并将查询分成两个不同的查询时,我注意到性能有了很大的提升,所以我假设我的 JOIN 没有优化。
结构:
-- tags
userId | tagId
1 3
1 4
2 3
2 9
-- search
userId | number | countryId | stateId ...
1 13 221 55
-- countries
countryId | countryName
221 Somewhere
-- users
userId | profileImageLink
1 | <photo link>
我正在尝试提取所有具有标签的用户,根据 search.number 排序并从其他表中获取元数据。查询:
SELECT
search.*, users.a, users.b, users.c, users.d, users.e, users.f, countries.location_country, states.location_state, cities.location_city
FROM search
RIGHT JOIN tags
ON search.user_id = tags.user_id
LEFT JOIN users
ON users.user_id=search.user_id
LEFT JOIN countries
ON countries.countryId=search.countryId
LEFT JOIN states
ON states.countryId=search.countryId AND states.stateId=search.stateId
LEFT JOIN cities
ON cities.countryId=search.countryId AND cities.stateId=search.stateId AND cities.cityId=search.cityId
WHERE
tags.skillId =52772
ORDER BY
search.number DESC LIMIT 0,200
我注意到将 JOIN 删除到 users 表(然后再这样做)会使查询更快。如何优化它以在同一个查询中工作?我尝试将 FROM 更改为标签而不是搜索,但这没有用...
这是 EXPLAIN 显示的:
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE tags ref skill_user,skillId skill_user 4 const 184854 Using index; Using temporary; Using filesort
1 SIMPLE search eq_ref user_id user_id 4 tags.user_id 1
1 SIMPLE countries eq_ref PRIMARY PRIMARY 2 search.countryId 1
1 SIMPLE states eq_ref PRIMARY,state PRIMARY 3 search.stateId 1
1 SIMPLE cities eq_ref PRIMARY,city PRIMARY 3 search.cityId 1
1 SIMPLE users eq_ref user_id user_id 4 search.user_id 1
EXPLAIN without the LEFT JOIN users:
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE tags ref skill_user,skillId skill_user 4 const 155870 Using index
1 SIMPLE search eq_ref user_id user_id 4 tags.user_id 1
1 SIMPLE countries eq_ref PRIMARY PRIMARY 2 search.countryId 1
1 SIMPLE states eq_ref PRIMARY,state PRIMARY 3 search.stateId 1
1 SIMPLE cities eq_ref PRIMARY,city PRIMARY 3 search.cityId 1
回答中建议的查询解释:
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE tags index NULL userid_skill 8 NULL 22689539 Using where; Using index; Using temporary; Using filesort
1 SIMPLE search eq_ref user_id user_id 4 tags.user_id 1
1 SIMPLE users eq_ref user_id user_id 4 search.user_id 1
1 SIMPLE countries eq_ref PRIMARY PRIMARY 2 search.countryId 1
1 SIMPLE states eq_ref PRIMARY,state PRIMARY 3 search.stateId 1
1 SIMPLE cities eq_ref PRIMARY,city PRIMARY 3 search.cityId 1