SQL自连接查询

我有四张桌子：

Service (serviceId(PK), serviceTypeId, capacity)
Facilitator (facilitatorId(PK), facilitatorName)
ServiceType (serviceTypeId(PK), serviceType)
ServiceFacilitator (serviceId(PK), facilitatorId(PK)) (join entity)

目前“服务类型”表中的服务类型为酒店和会议中心

“服务”表中的“容量”列包含的数字仅在与ServiceType.serviceTypeId相关时才有意义，即根据服务类型表示床或座位

我需要编写一个查询，它将返回3列，具体如下： 主持人姓名、床位、座位

我几乎可以肯定，在存储过程中创建和丢弃临时表是一个糟糕的解决方案，它可能会对未来的可伸缩性等产生负面影响，而且该解决方案涉及到服务表上的自连接

到目前为止，我的查询如下所示，但不返回任何行；我错过了什么

SELECT f.facilitatorName,(SUM(ts1.capacity)) as Beds,(SUM(ts2.capacity)) as Seats

FROM dbo.Facilitator as f,
        dbo.TestService as ts1,
        dbo.TestService as ts2,
        dbo.ServiceFacilitator as sf

WHERE f.facilitatorId = sf.facilitatorId AND
        (sf.serviceId = ts1.serviceId or
        sf.serviceId = ts2.serviceId) and 
        ts1.serviceId = ts2.serviceId and
        ts1.serviceTypeId = '1' and -- type hotel
        ts2.serviceTypeId = '2' -- type conference centre           

GROUP BY f.facilitatorName

将查询一分为二将返回床和座位的准确结果：

SELECT f.facilitatorName,(SUM(ts1.capacity)) as Beds

FROM dbo.Facilitator as f,
        dbo.TestService as ts1,
        dbo.ServiceFacilitator as sf

WHERE f.facilitatorId = sf.facilitatorId AND
        sf.serviceId = ts1.serviceId and 
        ts1.serviceTypeId = '1'         

GROUP BY f.facilitatorName

SELECT f.facilitatorName,(SUM(ts2.capacity)) as Seats

FROM dbo.Facilitator as f,
        dbo.TestService as ts2,
        dbo.ServiceFacilitator as sf

WHERE f.facilitatorId = sf.facilitatorId AND
        sf.serviceId = ts2.serviceId and 
        ts2.serviceTypeId = '2'         

GROUP BY f.facilitatorName

---

谢谢。

您的查询的简单解决方案应该是：

SELECT f.facilitatorName,
       SUM(case when ts.serviceTypeId = '1' then ts.capacity end) as Beds,
       SUM(case when ts.serviceTypeId = '2' then ts.capacity end) as Seats
FROM dbo.Facilitator as f
LEFT JOIN dbo.ServiceFacilitator as sf ON f.facilitatorId = sf.facilitatorId
LEFT JOIN dbo.TestService as ts ON sf.serviceId = ts.serviceId
GROUP BY f.facilitatorName

---

您应该对此查询使用Join。 例如：

SELECT f.facilitatorName,(SUM(ts1.capacity)) as Beds,(SUM(ts2.capacity)) as Seats

FROM 
        dbo.ServiceFacilitator as sf 
join dbo.Facilitator as f 
on   sf.facilitatorI = f.facilitatorId
join dbo.TestService as ts1 
on sf.serviceId = ts1.serviceId
join  dbo.TestService as ts1
on sf.serviceId = ts2.serviceId

WHERE 
        ts1.serviceTypeId = '1' and -- type hotel
        ts2.serviceTypeId = '2' -- type conference centre           

GROUP BY f.facilitatorName

---

可能值得一读，您正在使用的连接语法（ANSI 89）过时超过20年，在ANSI 92中被显式联接取代。链接实体

ServiceFacilitator

意味着每个服务可以有多个协导器-如果一个服务确实有多个协导器，是否存在任何类型的容量拆分？@Mark。。真的不确定；就在最后一分钟被拉进来了。还没有完全暴露在工作环境中。。。谢谢你抽出时间来看我。。