MySQL GROUP_CONCAT with Nulls

Question

Is there an option to make MySQL's Group_Concat function include nulls?

Consider the following example from my source table:

userId, questionId, selectionId 7, 3, NULL 7, 4, 1 7, 5, 2 

When I query on the selection table with GROUP_CONCAT, I get the following:

7, 4=1,5=2 

I would like to get the following:

7, 3=NULL,4=1,5=2 

For reference, my query looks like this:

Select userId, GROUP_CONCAT(CONCAT(questionId, '=', selectionId)) From selection Group by userId; 

I also tried adding an IFNULL like this:

Select userId, GROUP_CONCAT(IFNULL(CONCAT(questionId, '=', selectionId), 'NULL')) From selection Group by userId; 

but that produced the following:

7, NULL,4=1,5=2 

Note - There is one other complexity that I forgot to include. The selectionId is a foreign key to another table. I use a left outer join to the selection_text table. My real query includes fields from that table (these fields resolve to NULL since the selectionId is null).

Answer 1

You should just IFNULL the column that can be NULL;

SELECT userId, GROUP_CONCAT(CONCAT(questionId, '=',                   IFNULL(selectionId, 'NULL'))) FROM selection GROUP BY userId; 

Demo here.

Answer 2

You should use IFNULL or COALESCE on the selectionId value directly:

SELECT   userId,   GROUP_CONCAT(CONCAT(questionId, '=', COALESCE(selectionId, 'NULL'))) FROM selection GROUP BY userId;