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为了使这个查询更有效率，我希望可以消除嵌套的LEFT JOIN. 我考虑过是否可以替换COUNT(ActiveUsers)为COUNT(DISTINCT IF(SUM(grand_total)>0,id,NULL))以便我可以删除LEFT JOIN，但这似乎没有得到正确的结果。这是我正在使用的原始代码：

SELECT
COUNT(DISTINCT users.id) AS NumCustomer,
COUNT(ActiveUsers) AS NumActiveCustomers,
COUNT(ActiveUsers)/COUNT(DISTINCT username) AS CloseRate
FROM users
LEFT JOIN orders ON orders.userid = users.id
LEFT JOIN (SELECT id AS ActiveUsers FROM users LEFT JOIN orders ON orders.userid = users.id GROUP BY id HAVING SUM(grand_total)>0 ) AS Active ON users.id = Active.ActiveUsers
WHERE users.datecreated LIKE '2013%'
GROUP BY YEAR(users.created), MONTH(users.created)
ORDER BY YEAR(users.created), MONTH(users.created)

有没有办法让这段代码更有效率？

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1 回答 1

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如果 grand_total 不能为负：

SELECT
    COUNT(DISTINCT users.id) AS NumCustomer,
    COUNT(distinct orders.userid) AS NumActiveCustomers,
    COUNT(distinct orders.userid)/COUNT(DISTINCT users.username) AS CloseRate
FROM users
LEFT JOIN orders ON orders.userid = users.id
WHERE users.datecreated LIKE '2013%' and grand_total>0
GROUP BY YEAR(users.created), MONTH(users.created)
ORDER BY YEAR(users.created), MONTH(users.created)

（如果它也不能为零，那么你不需要第二个 where 条件。）

于 2013-10-13T12:42:50.193 回答