SQL JOIN WITH OR 条件

Question

我有一张表说 Cases，它使用来自 Workers 的参考来表示三列。还有一张 Company 员工所属的表。

下面是架构：

Cases [ CaseID, CaseNumber, Worker1, Worker2, Worker3 ] 
Workers [ WorkerID, ComapnyID]
Company [CompanyID, CompanyName]

现在我需要每个公司的案例计数。 那么是否可以与工人进行一次联接并映射所有 Worker1、Worker2 和 Worker3 列？有没有更好的选择和性能影响？

注意：一个公司的两名工人可以处理一个案件，或者所有工人都来自不同的公司。

Answer 1

虽然连接条件通常是相等性检查，但它们并没有什么特别之处 - 任何有效的 SQL 条件都可用于执行连接。在您的情况下，IN 条件似乎合适：

SELECT   CompanyName, COUNT(DISTINCT CaseID)
FROM     Company co
JOIN     Workers w ON co.CompanyId = w.CompanyId
JOIN     Cases ca ON w.WorkerId IN (ca.Worker1, ca.Worker2, ca.Worker3)
GROUP BY CompanyName

Answer 2

select
    C.CompanyID, C.CompanyName, count(distinct CaseID)
from Company C
    inner join Workers W
        on C.CompanyID = W.WorkerID
    inner join (
        select CaseId, WorkerId = Worker1 from Cases where Worker1 is not null
        UNION ALL
        select CaseId, WorkerId = Worker2 from Cases where Worker2 is not null
        UNION ALL
        select CaseId, WorkerId = Worker3 from Cases where Worker3 is not null
        ) CW
        on W.WorkerID = CW.WorkerID
group by C.CompanyID, C.CompanyName

Answer 3

我建议您像这样更改您的架构：

cases - caseid, casenumber
workers - workerid, companyid
cases_workers - caseid, workerid
company - companyid, companyname

如果你有这种方式，你可以写：

select companyname, count(*)
from company c
inner join workers w on c.companyid = w.companyid
inner join cases_workers cw on w.workerid = cw.workerid
group by companyname

编辑：

如果您无法更改架构，请使用其他评论者已经提到的一些好的查询。这是我的版本：

with caselist (
  select worker1 as worker from cases union all
  select worker2 as worker from cases union all
  select worker3 as worker from cases
)
select companyname, count(*)
from company c
inner join workers w on c.companyid = w.companyid
inner join caselist cl on w.workerid = cl.worker
group by companyname