相关疑难解决方法(0)

找到在同一天访问过两位同一专业的不同医生的患者.

示例数据库:单击此处查看SQL Fiddle中的示例数据脚本.

CREATE VIEW DistinctVisits AS
SELECT v.vid,v.pid,d.speciality,v.date
FROM Visits v ,Doctors d
WHERE d.did=v.did
GROUP BY v.pid,v.did,v.date;

CREATE VIEW DistinctVisits2 AS
SELECT dv.pid,dv.speciality,dv.date, COUNT(dv.vid) as countv
FROM DistinctVisits dv
GROUP BY dv.pid,dv.speciality,dv.date;

SELECT dv2.pid,dv2.speciality
FROM DistinctVisits2 dv2
WHERE dv2.countv=2;

DROP VIEW DistinctVisits;
DROP VIEW DistinctVisits2;

我如何重复相同的想法,但只是一个大问题？另外一个解决方案也会很好,但请尽量帮助我改进这个.