您有一个表,您希望根据该表计算两个不同表中的项目数。在这个例子中,我使用了建筑物,男人和女人
DROP TABLE IF EXISTS building;
DROP TABLE IF EXISTS men;
DROP TABLE IF EXISTS women;
CREATE TABLE building(name VARCHAR(255));
CREATE TABLE men(building VARCHAR(255), name VARCHAR(255));
CREATE TABLE women(building VARCHAR(255), name VARCHAR(255));
INSERT INTO building VALUES('building1');
INSERT INTO building VALUES('building2');
INSERT INTO building VALUES('building3');
INSERT INTO men VALUES('building1', 'andy');
INSERT INTO men VALUES('building1', 'barry');
INSERT INTO men VALUES('building2', 'calvin');
INSERT INTO men VALUES(null, 'dwain');
INSERT INTO women VALUES('building1', 'alice');
INSERT INTO women VALUES('building1', 'betty');
INSERT INTO women VALUES(null, 'casandra');
select
r1.building_name,
r1.men,
GROUP_CONCAT(women.name) as women,
COUNT(women.name) + r1.men_count as count
from
(select
building.name as building_name,
GROUP_CONCAT(men.name) as men,
COUNT(men.name) as men_count
from
building
left join
men on building.name=men.building
GROUP BY building.name) as r1
left join
women on r1.building_name=women.building
GROUP BY r1.building_name;有没有别的办法?上述方法的问题在于,子查询中两个表的列是隐藏的,需要在外部查询中重新声明。在两个单独的集合操作中创建不对称,而不存在不对称。我们同样可以先加入女性,然后加入男性。
发布于 2009-01-29 00:40:27
在SQL Server中,我只需要使用两个左连接来连接两个子查询-如果您想要的是对称性:
SELECT *
FROM building
LEFT JOIN (SELECT building, etc. FROM men GROUP BY etc.) AS men_summary
ON building.name = men_summary.building_name
LEFT JOIN (SELECT building, etc. FROM women GROUP BY etc.) AS women_summary
ON building.name = women_summary.building_name我倾向于使用首先声明的公用表表达式,而不是子查询-它的可读性更好(但不是ANSI -但GROUP_CONCAT也不是)。
发布于 2009-01-29 01:05:17
使用Union合并来自男性/女性表的数据
select building, [name] as menname, null as womenname from men
union
select building, null as menname, [name] as womenname from women现在,您在子查询中添加了一个‘表’,您可以对其进行连接、计数或其他操作。
顺便说一句,我明白为什么卡珊德拉被冷落了,因为没有人相信她,但是德文呢,他也同样被众神诅咒了吗?
https://stackoverflow.com/questions/490053
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