MySQL - For each Row Print Columns/Flags with value equal to 1

One of my colleague came to me with this problem. It enjoyed solving it. Here, it is for you. Say, you are given a table like this with a given number of columns.

   id  Flag_1  Flag_2  Flag_3  Flag_4  Flag_5

------  --------  -------  --------  --------  -------

    1       1       1       1       1         1

    2       0       0       0       0         0

    3       1       1       0       1         0

    4       0       1       0       0         1

    5       1       0       1       0         1

Desired output is to have a comma separated list of "Flag Names" that are ON for each row. i.e.

   id  onFlags                             

------  ------------------------------------

    1  Flag_1,Flag_2,Flag_3,Flag_4,Flag_5  

    2                                      

    3  Flag_1,Flag_2,Flag_4,               

    4  Flag_2,Flag_5                       

    5  Flag_1,Flag_3,Flag_5   

It's not a generally required to print column names as a result of query. One easy solution is to fetch data in sql and then use some programming language to manipulate it. However, try running sql only to fetch it. I recommend to minimize the browser and try it on your own.

=============================================

SELECT

 id, CONCAT(flag1, flag2, flag3, flag4,flag5) AS onFlags

FROM

 (SELECT

   IF(Flag_1 = '1', 'Flag_1,', '') AS flag1,

   IF(Flag_2 = '1', 'Flag_2,', '') AS flag2,

   IF(Flag_3 = '1', 'Flag_3,', '') AS flag3,

   IF(Flag_4 = '1', 'Flag_4,', '') AS flag4,

   IF(Flag_5 = '1', 'Flag_5', '') AS flag5,

   id

 FROM

   Flags) AS a ;