How to combine multiple columns as one and format with custom strings?

What about the CONCAT() function?

SELECT id, CONCAT(lastname, ', ', firstname) AS name FROM `table`;

If you are going to concatenate many fields, you could also consider the CONCAT_WS() function, where the first argument is the separator for the rest of the arguments, which is added between the strings to be concatenated:

SELECT id, 
       CONCAT_WS(',', field_1, field_2, field_3, field_4) list
FROM   `table`;