檢索使用條件

Question

從2個表的數據我有2個表

+---------------------+ 
|  T_EQUIPMENT | 
+----+--------+---+---+ 
| ID | NAME |APPROVED| 
+----+--------+---+---+ 
| 01 | foo1 | 0 | 
+----+--------+---+---+ 
| 02 | foo2 | 1 | 
+----+--------+---+---+ 
| 03 | foo3 | 1 | 
+----+--------+---+---+ 
| 04 | foo4 | 1 | 
+----+--------+---+---+ 

+---------------------------+ 
|  T_HAS_EQUIPMENT  | 
+----+------------+----+----+ 
| ID_CENTER | ID_EQUIP  | 
+----+------------+----+----+ 
|  12 |  2  | 
+----+------------+----+----+ 
|  3  |  3  | 
+----+------------+----+----+ 
|  3  |  2  | 
+----+------------+----+----+ 
|  5  |  3  | 
+----+-----------+----+----+ 
|  6  |  2  | 
+----+------------+----+----+ 

我想要得到的ID，覈準的設備（認可= 1）的名稱，但也不論這個特定的中心有此設備

例如用於id_center = 3，我想這

+---------------------+ 
    |  RESULT  | 
    +----+--------+---+---+ 
    | ID | NAME | HAS | 
    +----+--------+---+---+ 
    | 02 | foo2 | 1 | 
    +----+--------+---+---+ 
    | 03 | foo3 | 1 | 
    +----+--------+---+---+ 
    | 04 | foo4 | 0 | 
    +----+--------+---+---+ 

所以，我檢索所有的設備，我知道一箇中心是否有此設備。有任何想法嗎？

Answer 1

使用：

SELECT e.id, 
      e.name, 
      CASE 
      WHEN he.id_center IS NOT NULL THEN 1 
      ELSE 0 
      END AS has 
    FROM T_EQUIPMENT e 
LEFT JOIN T_HAS_EQUIPMENT he ON he.id_equip = e.id 
          AND he.id_center = 3 
    WHERE e.approved = 1 
ORDER BY e.id 

使用外部（左，右）濾波器的Placement條件對錶加入可以顯着改變它的輸出。在此示例中，id_center在JOIN創建之前被過濾。如果它在WHERE子句中，則將在之後應用過濾。