mysql - LEFT JOIN 显示不在右表中的记录

Question

我有两个表 ECRDTL_del 和 ECRDTL_edit，我只想显示 ECRDTL_del 中不在 ECRDTL_edit 中的记录。 我试过使用 MYSQL left join，但无法得到想要的结果。这是我当前的查询字符串:

SELECT a.*
FROM ECRDTL_del AS a
    LEFT JOIN ECRDTL_edit AS b ON b.Ecrno = a.Ecrno
WHERE b.Cylno <> a.Cylno

下面提到的这两个表的数据示例和预期结果:

ECRDTL_del:

Ecrno  Cylno
9090   8881
9090   8882
9090   8883
9090   8884

ECRDTL_edit:

Ecrno  Cylno
9090   8881
9090   8885
9090   8886
9090   8884

LEFT 连接后的预期结果:

Ecrno  Cylno
9090   8882
9090   8883

Answer 1

从你的问题:

"...I want to display only records from ECRDTL_del which are not in ECRDTL_edit."

你很接近，你只需要检查 b.Ecrno IS NULL。

SELECT a.* 
FROM   ECRDTL_del AS a 
       LEFT JOIN ECRDTL_edit AS b 
          ON a.Ecrno = b.Ecrno AND 
             a.Cylno = b.Cylno
WHERE  b.Ecrno IS NULL

• SQLFiddle Demo

输出

╔═══════╦═══════╗
║ ECRNO ║ CYLNO ║
╠═══════╬═══════╣
║  9090 ║  8882 ║
║  9090 ║  8883 ║
╚═══════╩═══════╝