LeftJoin減號（右表數據+內連接數據）

Question

表1）
m_conservationsetting

+------------+-------+------------+ 
| FacilityId | Unit | CategoryId | 
+------------+-------+------------+ 
|  1  | 1 |  1  | 
|  1  | 1 |  2  | 
|  1  | 1 |  3  | 
|  1  | 2 |  1  | 
|  1  | 2 |  2  | 
|  2  | 1 |  1  | 
|  2  | 2 |  1  | 
+------------+-------+------------+ 

唯一密鑰（FacilityId單位的CategoryId）

表2）的
l_maintelog

+------------+------+------------+--------+ 
| FacilityId | Unit | CategoryId | Status | 
+------------+------+------------+--------+ 
| 1  | 1 |  1  | 0 | 
| 1  | 1 |  2  | 1 | 
| 1  | 1 |  3  | 0 | 
| 1  | 2 |  1  | 0 | 
| 2  | 1 |  1  | 0 | 
| 2  | 2 |  1  | 0 | 
+------------+------+------------+--------+ 

結果：

+------------+------+------------+ 
| FacilityId | Unit | CategoryId | 
+------------+------+------------+ 
|  1  | 1 |  2  | 
|  1  | 2 |  2  | 
+------------+------+------------+ 

表1需要被留下了表2加入，它應該ommit連接結果，僅顯示table1的數據結果。
Table1 LeftJoin Table2 - （join Data）for the following query。用於獲取結果的條件是檢查狀態= 0備案表2中

查詢

select cs.FacilityId,Cs.Unit,cs.CategoryId 
from m_conservationsetting cs 
LEFT JOIN l_maintelog ml on 
(cs.FacilityId=ml.FacilityId and cs.Unit=ml.Unit) 
WHERE (ml.Status=0 
) 
group by cs.CategoryId 

Answer 1

您可以使用第二個表的鍵列NULL條件，以消除結果是有兩個表中

Select cs.FacilityId,Cs.Unit,cs.CategoryId 
from m_conservationsetting cs 
LEFT JOIN l_maintelog ml on 
(cs.FacilityId=ml.FacilityId and cs.Unit=ml.Unit) 
WHERE (ml.Status=0 
and ml.FacilityId IS NULL) 
group by cs.CategoryId