Mysql 如何使用count函数从不同的表中减去2列?
目前,我正在使用count函数计算两列的值,并希望减去这两列并导出到excel文件 这是我的密码。我认为粗体陈述包含逻辑错误Mysql 如何使用count函数从不同的表中减去2列?,mysql,sql,count,subquery,left-join,Mysql,Sql,Count,Subquery,Left Join,目前,我正在使用count函数计算两列的值,并希望减去这两列并导出到excel文件 这是我的密码。我认为粗体陈述包含逻辑错误 SELECT software.*, (SELECT count(lkey.k_id) FROM lkey WHERE lkey.s_id = software.s_id) AS Total, (SELECT count(assign.k_id) FROM assign WHERE assign.s_id = software.s_id) AS Installed,
SELECT software.*,
(SELECT count(lkey.k_id) FROM lkey WHERE lkey.s_id = software.s_id) AS Total,
(SELECT count(assign.k_id) FROM assign WHERE assign.s_id = software.s_id) AS Installed,
**(SELECT count(lkey.k_id) - count(assign.k_id) FROM lkey INNER JOIN assign
WHERE lkey.k_id = assign.k_id GROUP BY lkey.k_id) AS Available**
FROM software";
我想在聚合查询中需要两个
左连接
s:
SELECT s.*,
COALESCE(l.total, 0) total,
COALESCE(a.installed, 0) installed,
COALESCE(l.total, 0) - COALESCE(a.installed, 0) available
FROM software s
LEFT JOIN (SELECT s_id, count(*) total FROM lkey GROUP BY s_id) l
ON l.s_id = s.s_id
LEFT JOIN (SELECT s_id, count(*) installed FROM assign GROUP BY s_id) a
ON a.s_id = s.s_id
在MySQL的最新版本中,您可以使用横向连接:
SELECT s.*, l.total, a.installed, l.total - a.installed available
FROM software s
LEFT JOIN LATERAL (SELECT count(*) total FROM lkey l WHERE l.s_id = s.s_id) l ON 1
LEFT JOIN LATERAL (SELECT count(*) installed FROM assign a WHERE a.s_id = s.s_id) a ON 1
非常感谢。我已经解决了这个问题。