Variable gets not substituted by its value - mysql

Question

I want to insert data from table AnswerSets
+-------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| Id | int(11) | YES | | NULL | |
| Q1 | int(11) | YES | | NULL | |
| Q2 | int(11) | YES | | NULL | |
| Q3 | int(11) | YES | | NULL | |
[...]
+-------+---------+------+-----+---------+-------+
to T_ANSWER_SET.
+--------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------+---------+------+-----+---------+-------+
| U_ID | int(11) | YES | | NULL | |
| Q_ID | int(11) | YES | | NULL | |
| ANSWER | int(11) | YES | | NULL | |
+--------+---------+------+-----+---------+-------+
Therefor I use the following query in a loop in a procedure:
INSERT INTO T_ANSWER_SET (U_ID, Q_ID, ANSWER)
SELECT i, j, (SELECT c FROM AnswerSets WHERE Id = i);
i, j are integers and are used are incremented in a loop. c is a name of a column (like 'Q10') of AnswerSets from which I want the data. But I get always this:
+------+------+--------+
| U_ID | Q_ID | ANSWER |
+------+------+--------+
| 1 | 1 | 0 |
| 1 | 2 | 0 |
| 1 | 3 | 0 |
[...]
+------+------+--------+
What I want the query to do for i =3, j = 10 and c = 'Q10':
INSERT INTO T_ANSWER_SET (U_ID, Q_ID, ANSWER)
SELECT 3, 10, (SELECT Q10 FROM AnswerSets WHERE Id = 3);
Thanks in advance for your help.

Answer 1

Try PREPARE Statement:
MariaDB [(none)]> SET #`i` := 3,
-> #`j` := 1,
-> #`c` := '`Q10`';
Query OK, 0 rows affected (0.00 sec)
MariaDB [(none)]> SET #`stmt` := CONCAT('
'> INSERT INTO `T_ANSWER_SET` (`U_ID`, `Q_ID`, `ANSWER`)
'> SELECT ', #`i`, ', ', #`j`, ', (SELECT ', #`c`, '
'> FROM `AnswerSets`
'> WHERE `Id` = ', #`i`, ')
'> ');
Query OK, 0 rows affected (0.00 sec)
MariaDB [(none)]> SELECT #`stmt`;
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| #`stmt` |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
|
INSERT INTO `T_ANSWER_SET` (`U_ID`, `Q_ID`, `ANSWER`)
SELECT 3, 1, (SELECT `Q10`
FROM `AnswerSets`
WHERE `Id` = 3)
|
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
MariaDB [(none)]> -- PREPARE `stmt` FROM #`stmt`;
MariaDB [(none)]> -- EXECUTE `stmt`;
MariaDB [(none)]> -- DEALLOCATE PREPARE `stmt`;