Using COUNT in GROUP_CONCAT

You can also achieve that by counting the number of commas (or whatever's your separator) in the GROUP_CONCAT:

SELECT (LENGTH(GROUP_CONCAT(DISTINCT fk_company))-LENGTH(REPLACE(GROUP_CONCAT(DISTINCT fk_company), ',', '')))
FROM `table`
GROUP BY fk_company

You need to COUNT() with GROUP BY in an inner SELECT clause first and then apply GROUP_CONCAT();

SELECT GROUP_CONCAT(cnt) cnt
FROM (
    SELECT COUNT(*) cnt
    FROM table1
    GROUP BY fk_company
) q;

Output:

|   CNT   |
-----------
| 3,2,3,1 |

Here is SQLFiddle demo.

Related