Question

How do I prefix a string to a field before GROUP_CONCAT

this

id       test_id         
1           4              
2           4             
2           5            
3           5           
1           5
1           6

to

id       test_id         
1           id_4,id_5,id_6              
2           id_4,id_5             
3           id_5            

I want id_ prefixed to the test_id before I can get it by GROUP_CONCAT in MySQL

Answer 1

SELECT
  id,
  GROUP_CONCAT(CONCAT('id_', test_id))
FROM
  your_table
GROUP BY id