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
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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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