MySQL select column which is a value in another column

Question

my sql table is something like this:

+----+------------+--------+---------------+---------------+-------------+----------+-------------+---------------------+
| id | msisdn     | status | reason        | CallRejection | Unavailable | NoAnswer | NetworkBusy | autotimestamp       |
+----+------------+--------+---------------+---------------+-------------+----------+-------------+---------------------+
|  1 | 9999999901 | Failed | NoAnswer      |             1 |           2 |        2 |           4 | 2013-12-19 15:46:50 |
|  2 | 9999999902 | Failed | NetworkBusy   |             4 |           2 |        3 |           2 | 2013-12-19 13:07:42 |
|  3 | 9999999903 | Failed | CallRejection |             6 |           6 |        6 |           5 | 2013-12-19 13:07:53 |
|  4 | 9999999904 | Failed | Unavailable   |             2 |           4 |        2 |           0 | 2013-12-19 13:08:03 |
|  5 | 9999999905 | Failed | Misc          |             6 |           2 |        6 |           2 | 2013-12-19 13:07:01 |
|  6 | 9999999906 | Failed | NoAnswer      |             1 |           3 |        1 |           6 | 2013-12-19 13:07:24 |
|  7 | 9999999907 | Failed | NetworkBusy   |             6 |           6 |        2 |           3 | 2013-12-19 13:07:42 |
|  8 | 9999999908 | Failed | CallRejection |             8 |           3 |        3 |           0 | 2013-12-19 13:07:53 |
|  9 | 9999999909 | Failed | Unavailable   |             3 |           8 |        5 |           6 | 2013-12-19 13:08:03 |
| 10 | 9999999910 | Failed | Misc          |             8 |           4 |        0 |           4 | 2013-12-19 13:07:01 |
+----+------------+--------+---------------+---------------+-------------+----------+-------------+---------------------+

I want to extract the value of each reason based on the value of reason column for each row. eg:

row 1 should give 2 as a result because the reason column has noanswer , so the value of that particular column ie noanswer should be returned.

Actually, I have to select multiple rows after comparing the returned valued with a constant. I'm able to do this by the following method :

select @col := reason from msisdn_table where id=1;
SET @a = concat('select ', @col, ' from msisdn_table where id=1');
PREPARE STMT FROM @a;
EXECUTE STMT;
DEALLOCATE PREPARE STMT;

But this is not very promising solution because it is for only one row and i'll have to use a for loop in order to get chunk's of 1000 rows, and that would not be very efficient. What is the more efficient way?

Answer 1

Try this:

SELECT id, 
       reason
       CASE
         WHEN reason = 'NoAnswer' THEN NoAnswer
         WHEN reason = 'NetworkBusy' THEN NetworkBusy
       END AS value
FROM table1

It should give you an output like this:

+----+------------+----------+
| id | reason     | value    |
+----+------------+----------+
|  1 | NoAnswer   |        2 |
+----+------------+----------+