如何比较同一个表 (SQL Server) 中的 2 行? [英] How do I compare 2 rows from the same table (SQL Server)?

问题描述

我需要创建一个后台作业来处理一个表，以查找在具有不同状态的特定 id 上匹配的行.它将行数据存储在一个字符串中，以将数据与具有匹配 id 的行进行比较.

I need to create a background job that processes a table looking for rows matching on a particular id with different statuses. It will store the row data in a string to compare the data against a row with a matching id.

我知道获取行数据的语法，但我以前从未尝试过比较同一个表中的 2 行.它是如何完成的?我是否需要使用变量来存储每个变量的数据?或者其他方式?

I know the syntax to get the row data, but I have never tried comparing 2 rows from the same table before. How is it done? Would I need to use variables to store the data from each? Or some other way?

(使用 SQL Server 2008)

(Using SQL Server 2008)

推荐答案

你可以根据需要多次加入一个表，它被称为 自加入.

You can join a table to itself as many times as you require, it is called a self join.

为表的每个实例分配一个别名(如下例所示)以区分一个.

An alias is assigned to each instance of the table (as in the example below) to differentiate one from another.

SELECT a.SelfJoinTableID
FROM   dbo.SelfJoinTable a
       INNER JOIN dbo.SelfJoinTable b
         ON a.SelfJoinTableID = b.SelfJoinTableID
       INNER JOIN dbo.SelfJoinTable c
         ON a.SelfJoinTableID = c.SelfJoinTableID
WHERE  a.Status = 'Status to filter a'
       AND b.Status = 'Status to filter b'
       AND c.Status = 'Status to filter c' 

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