将RIGHT外部联接转换为left外部联接sqlite [英] convert RIGHT outer join to left outer join sqlite

问题描述

我需要为Sqlite设计查询 原始查询就是这样

i need to design a query for Sqlite the original query was like this

 FROM            PhysicianActivity INNER JOIN
                     Activity ON PhysicianActivity.ActivityID = Activity.ID RIGHT OUTER JOIN
                     PhysicianFrequency ON PhysicianActivity.PhysicianID = PhysicianFrequency.PhysicianID AND Activity.LegalEntityID = PhysicianFrequency.LegalEntityID 

知道sqlite不支持RIGHT OUTER JOIN，所以我被LEFT OUTER JOIN困住了，但是我无法将此查询转换为LEFT OUTER JOIN

knowing that sqlite doesn't support RIGHT OUTER JOIN so i am stuck with LEFT OUTER JOIN but i can't convert this query to LEFT OUTER JOIN

任何人都可以帮忙吗?

推荐答案

大多数人都喜欢LEFT OUTER JOIN.在大多数情况下，以下是等效的:

Most people prefer LEFT OUTER JOIN. The following is equivalent under most circumstances:

FROM  PhysicianFrequency LEFT JOIN
      PhysicianActivity 
      ON PhysicianActivity.PhysicianID = PhysicianFrequency.PhysicianID LEFT JOIN
      Activity
      ON PhysicianActivity.ActivityID = Activity.ID AND
         Activity.LegalEntityID = PhysicianFrequency.LegalEntityID 

我建议您使用表别名，以便查询更易于编写和阅读:

I would recommend that you use table aliases so the query is easier to write and to read:

FROM  PhysicianFrequency pf LEFT JOIN
      PhysicianActivity pa
      ON pa.PhysicianID = pf.PhysicianID LEFT JOIN
      Activity a
      ON pa.ActivityID = a.ID AND
         a.LegalEntityID = pf.LegalEntityID

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