SQLite的：SELECT語句，並顯示`null`值太大

Question

我還有一個情況下，我正在尋找一個查詢，可以顯示null值太大，

首先在所有的，我讓表1;

+---------+----------+ 
|id_table1| value | 
+---------+----------+ 
| 1  | value1 | 
| 2  | value2 | 
| 3  | value3 | 
| 4  | value4 | 
| 5  | value5 | 
| 6  | value6 | 
| 7  | value7 | 
| 8  | value8 | 
| 9  | value9 | 
+---------+----------+ 

表2：

+---------+----------+ 
|id_table1| value | 
+---------+----------+ 
| P1 | valueP1 | 
| P2 | valueP2 | 
+---------+----------+ 

，這是我的關係表：

+---------+----------+---------+ 
|id_boss | id_child | answ | 
+---------+----------+---------+ 
| 1  |  2 | T | 
| 1  |  6 | F | 
| 2  |  P1 | T | 
| 2  |  4 | F | 
| 6  |  P2 | T | 
| 6  |  8 | F | 
+---------+----------+ --------+ 

我下面這個真棒answer，使我第一次查詢的工作，CEK這SQLFiddle

+---------+-----------+-----------+ 
|id_boss | child_T | child_F |  
+---------+-----------+-----------+ 
| value1 | value2 | value6 | 
| value2 | valueP1 | value4 | 
| value6 | valueP2 | value8 | 
+---------+-----------+-----------+ 

然後在這裏是我的新問題，

從關係表， 讓的說，我刪除一些id_child價值，所以後來我就可以填滿它，

+---------+----------+---------+ 
|id_boss | id_child | answ | 
+---------+----------+---------+ 
| 1  |  2 | T | 
| 1  |  6 | F | 
| 2  |  P1 | T | 
| 2  |  4 | F | 
| 6  |   | T | 
| 6  |   | F | 
| 4  |   | T | 
| 4  |   | F | 
+---------+----------+ --------+ 

，然後我正在尋找一種方式讓我的查詢是這樣的：

+---------+-----------+-----------+ 
|id_boss | child_T | child_F |  
+---------+-----------+-----------+ 
| value1 | value2 | value6 | 
| value2 | valueP1 | value4 | 
| value6 | `null` | `null` | 
| value4 | `null` | `null` | 
+---------+-----------+-----------+ 

Answer 1

試試這個：

SELECT (SELECT value FROM table1 WHERE table1.id_table1 = r1.id_boss) AS id_boss, 
    COALESCE((SELECT value FROM table1 WHERE table1.id_table1 = r1.id_child), 
       (SELECT value FROM table2 WHERE table2.id_table2 = r1.id_child) 
      ) AS child_T, 
    COALESCE((SELECT value FROM table1 WHERE table1.id_table1 = r2.id_child), 
       (SELECT value FROM table2 WHERE table2.id_table2 = r2.id_child) 
      ) AS child_F 
FROM r_table AS r1 , r_table AS r2 
WHERE r1.id_boss = r2.id_boss AND r1.answ = 'T' AND r2.answ = 'F'; 

SQL Fiddle

它適用於我，但如果您有問題，請告訴我。