How do I stop a comma being added using CONCAT_WS if column is empty

Question

SELECT CONCAT_WS(',', Col1, Col2, Col3 ) AS combined FROM table_name

Currently if I have fields Col1 = 'hello', Col2 = 'Bye', Col2 = 'Goodnight'

The above select statement would return hello,Bye,Goodnight which is fine.

What if any of the Cols where blank. A Comma would still be added. like hello,,Goodnight.

Is there a way to say if the Col is empty then ignore it? (This is MySQL)

Answer 1

Function CONCAT_WS ignores NULL values and doesn't generate a separator if either of its arguments is NULL.

For empty, i.e. equal to '', values you can use NULLIF:

SELECT CONCAT_WS(',', NULLIF(Col1, ''), NULLIF(Col2, ''), NULLIF(Col3, '') ) AS combined 
FROM table_name