I'm running two queries on a view. Both group by the same set of columns (a,b,c) and count the values of a fourth column d. When using COUNT(d), the query returns 13 rows. When using COUNT(Dinstinct d), the queries returns >30 rows, most of them have count(d)=1. Obviously, the latter output is wrong.

Using distinct works when skipping the ORDER BY clause or using the same column ordering in the order by clause as with the group by clause.

Works:

SELECT a,b,c , count( d ) FROM someView
GROUP BY a,b,c
ORDER BY c,a,b
LIMIT 0,30

Works:

SELECT a,b,c , count(distinct d ) FROM someView
GROUP BY a,b,c
ORDER BY a,b,c
LIMIT 0,30

Broken:

SELECT a,b,c , count(distinct d ) FROM someView
GROUP BY a,b,c
ORDER BY c,a,b
LIMIT 0,30

I'm using MariaDB 10.0.22-MariaDB-0+deb8u1 - (Debian). This used to work with MySQL 5 and maybe MariaDB 5.