SQLite : Select statement and show `null` value too

Question

i have another case , i'm looking a query that can show null value too,

first at all, i make table1;

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

table2:

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

and this is my relationship table:

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

i following this awesome answer to make my first query work, cek this SQLFiddle

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

and then here's my new problem,

from relationship table, let say, i'm removing some id_child value, so i can fill it later,

+---------+----------+---------+
|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    |
+---------+----------+ --------+

and then i'm looking a way to make my query look like this :

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

Answer 1

Try this:

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

It works for me but if you have a problem let me know.