Fetching the columns of a MySQL table based on the values of the column

Question

I'm trying to retrieve the column names of a table of the following format:

id | error 1 | error 2 | error 3 | error 4 |
--------------------------------------------
 1 |    1    |    0    |    0    |    1    |
-------------------------------------------
 2 |    0    |    0    |    0    |    0    |

I need to retrieve the column name whose value is 1. Instead of doing "Select * from table where id = 'someid'" and then filtering out, is there a way to hit the column names directly from the query?

Answer 1

Although it would be MUCH better to just do a normal SQL query and then process the data in your PHP code, you can use CASE clauses here to get it done in SQL:

SELECT id,
  ( CASE WHEN `error 1` = 1 THEN 'error 1' END ),
  ( CASE WHEN `error 2` = 1 THEN 'error 2' END ),
  ( CASE WHEN `error 3` = 1 THEN 'error 3' END ),
  ( CASE WHEN `error 4` = 1 THEN 'error 4' END )
  FROM your_table

Answer 2

SELECT id, CONCAT_WS(',',t2.e1,t2.e2,t2.e3,t2.e4) as err FROM table1
INNER JOIN (
  SELECT id, 
    CASE WHEN `error 1`= 1 THEN 'error 1' ELSE NULL END AS e1,
    CASE WHEN `error 2`= 1 THEN 'error 2' ELSE NULL END AS e2,
    CASE WHEN `error 3`= 1 THEN 'error 3' ELSE NULL END AS e3,
    CASE WHEN `error 4`= 1 THEN 'error 4' ELSE NULL END AS e4
  FROM table1

) as t2
on table1.id=t2.id