Rows with null value for group_concat not returned

Question

I've got the following MySQL query that's supposed to return records from table a and b (one to many relationship), and also a comma seperated list of any values returned from table c. However, there won't always be records in table c (which is why I'm using a LEFT OUTER JOIN to join it to table a).

SELECT  `a`.`id` , `a`.`name` , `b`.`id` AS  `b_id` , `b`.`name` AS  `b_name` , GROUP_CONCAT(  `c`.`l_id` ) AS  `c_ls`
FROM  `a`
INNER JOIN  `b` ON  `a`.`b_id` =  `b`.`id`
LEFT OUTER JOIN  `c` ON  `a`.`id` = `c`.`a_id`
GROUP BY `a`.`id`
ORDER BY  `a`.`created` DESC

The query above returns 1 record when it should return 2. Record 1 has 3 matching records in table c, record 2 has 0 matching records in table c.

The query returns:

id | name | b_id | b_name | c_ls
1  | John |   2  |  Bla   | [BLOB - 3 B]

If I remove the GROUP_CONCAT and GROUP_BY clauses then it returns 2 records:

id | name | b_id | b_name | c_ls
1  | John |   2  |  Bla   | [BLOB - 3 B]
2  | Fred |   3  |  Blo   | [BLOB - NULL]

It seems that if c_ls is null then GROUP_CONCAT stops the row from being returned. Any thoughts as to what I'm doing wrong?

Answer 1

The answer previously marked as right is unfortunately wrong (as user desaivv noted in the comment).

It must read IFNULL, [not ISNULL, isnull just takes one parameter and returns a boolean] !

IFNULL returns the second paramter if null:

SELECT  `a`.`id` , `a`.`name` , `b`.`id` AS  `b_id` , `b`.`name` AS  `b_name` ,   
IFNULL(GROUP_CONCAT(  `c`.`l_id` ), '') AS  `c_ls`
FROM  `a`
INNER JOIN  `b` ON  `a`.`b_id` =  `b`.`id`
LEFT OUTER JOIN  `c` ON  `a`.`id` = `c`.`a_id`
GROUP BY `a`.`id`
ORDER BY  `a`.`created` DESC

But this is not the solution at all! What we need is a "convoluted" join -

So please check this SQL Fiddle: http://www.sqlfiddle.com/#!2/54c6f/3/0