使用左连接是null而不是mysql中不存在的位置

I cannot change my code to left join is null while I am trying use where in table2. Please see my query bellow

当我尝试在table2中使用where时,我无法将我的代码更改为left join is null。请看下面的查询

      SELECT  table1.column1,  table1.column2
      FROM table1
          WHERE NOT 
              EXISTS (
                    SELECT table2.column1, table2.column2
                    FROM table2
                    WHERE table2.column1= table1.column1
                    AND table2.location_id= 6
                )
      GROUP BY Barcode

Can you please explain even it's not useful or bad question. It is my real problem.

你能解释一下,即使这不是有用或不好的问题。这是我真正的问题。

1 个解决方案

#1

Why can't you use left join?

为什么你不能使用左连接?

SELECT  table1.column1,  table1.column2
   FROM table1
   LEFT JOIN table2
   ON table2.column1= table1.column1
     AND table2.location_id= 6
   WHERE table2.column1 is null
   GROUP By Barcode

Also, your assumption that left join is better is not necesarrily correct. The article linked by TsSkTo in the comments to your question shows that left join is a worse solution for MSSQL

此外,您认为左连接更好的假设并不是必须正确的。 TsSkTo在你的问题评论中链接的文章表明,左连接对于MSSQL来说是一个更糟糕的解决方案

#1