mysql - 带有子查询和 "HAVING"的极慢 SQL 查询

Question

我有这个查询，我想计算“用户”中有多少条目在“用户名”中有多个条目

SELECT usernames.NAME,
    COUNT(user.id)
FROM user
INNER JOIN user_username ON user.id = user_username.user_id
INNER JOIN usernames ON user_username.user_username_id = usernames.id
WHERE 
    user.datecreated BETWEEN '2016-01-01' AND '2016-09-01'
    AND user.id IN 
        (
            SELECT user_id
            FROM user_username
            GROUP BY user_id
            HAVING COUNT(*) > 1
        )
GROUP BY usernames.NAME
ORDER BY user.id DESC

查询有效，但速度太慢，有什么想法可以加快查询速度吗？

Answer 1

像这样分解查询有帮助吗？

CREATE TEMPORARY TABLE QualifiedUserIDs AS (
SELECT user_id
FROM user_username
GROUP BY user_id
HAVING COUNT(*) > 1);

SELECT usernames.NAME,
    COUNT(user.id)
FROM user
INNER JOIN QualifiedUserIDs quids ON quids.user_id = user.id 
INNER JOIN user_username ON user.id = user_username.user_id
INNER JOIN usernames ON user_username.user_username_id = usernames.id
WHERE 
    user.datecreated BETWEEN '2016-01-01' AND '2016-09-01'

GROUP BY usernames.NAME
ORDER BY user.id DESC