我正在修改现有项目。我想将 3 个 mysql 请求合并为一个。
这3个请求具有相同的选定数据,只是WHERE发生变化。 这是示例请求之一:
SELECT COUNT(seg.my_seg1) FROM (
SELECT COUNT(DISTINCT cp.conference_id) as my_seg1 FROM A.Account a
INNER JOIN A.ConferenceParticipant cp ON a.account_id = cp.user_id
INNER JOIN A.Conference cf ON cf.id = cp.conference_id
WHERE cf.`status` = 0
AND DATE_SUB(CURDATE(), INTERVAL 30 DAY) <= cf.creation_timestamp
GROUP BY a.account_id) as seg
WHERE seg.my_seg1 >= 30
其他 2 个请求完全相同,除了:
WHERE seg.my_seg1 >= 11 AND seg.my_seg1 <= 30;
和:
WHERE seg.my_seg1 >= 30;
所以我的问题是如何根据同一请求中的 WHERE 结果获得 3 个不同的值?
最佳答案
这样您将拥有 3 个虚拟列:
SELECT
COUNT(IF(seg.my_seg1 >= 30, 1, 0)) AS res1,
COUNT(IF(seg.my_seg1 >= 11 AND seg.my_seg1 < 30, 1, 0)) AS res2
FROM (
SELECT COUNT(DISTINCT cp.conference_id) as my_seg1
FROM A.Account a
JOIN A.ConferenceParticipant cp ON a.account_id = cp.user_id
JOIN A.Conference cf ON cf.id = cp.conference_id
WHERE
cf.`status` = 0
AND DATE_SUB(CURDATE(), INTERVAL 30 DAY) <= cf.creation_timestamp
GROUP BY a.account_id
) AS seg
但是你必须修改你的过滤器,你说的是 3 个,但我只看到 2 个不同的。
关于MySQL : Different behaviors depending on WHERE result,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/17149742/