如何在 SQL Server 中的两个 SELECT 语句之间执行 LEFT JOIN? [英] How to perform a LEFT JOIN in SQL Server between two SELECT statements?

问题描述

我在 SQL Server 中有两个 SELECT 语句，如下所示:

I have two SELECT statements in SQL Server like these:

(SELECT [UserID] FROM [User])
(SELECT [TailUser], [Weight] FROM [Edge] WHERE [HeadUser] = 5043)

我想在 [UserID] 属性和 [TailUser] 属性的这两个 SELECT 语句之间执行 LEFT JOIN.我想将第二个查询中的现有记录与第一个查询中的相应记录和缺失记录的 NULL 值连接起来.我该怎么做?

I want to perform a LEFT JOIN between these two SELECT statements on [UserID] attribute and [TailUser] attribute. I want to join existent records in second query with the corresponding records in first query and NULL value for absent records. How can I do this?

推荐答案

SELECT * FROM 
(SELECT [UserID] FROM [User]) a
LEFT JOIN (SELECT [TailUser], [Weight] FROM [Edge] WHERE [HeadUser] = 5043) b
ON a.UserId = b.TailUser

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