MySQL 5.7: Order by left-joined one-to-many tables - mysql

Question

Database
mysql> DESCRIBE filtercategories;
+----------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(16) | NO | | NULL | |
| position | tinyint(4) | NO | | NULL | |
+----------+-------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)
mysql> DESCRIBE tags;
+---------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| slug | varchar(64) | NO | UNI | NULL | |
| name | varchar(128) | NO | | NULL | |
| color | varchar(7) | NO | | NULL | |
| visible | tinyint(1) | NO | | 0 | |
+---------+--------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)
mysql> DESCRIBE filtercategories_tags;
+-------------------+------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------------------+------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| filtercategory_id | int(11) | NO | MUL | NULL | |
| tag_id | int(11) | NO | MUL | NULL | |
| position | tinyint(4) | NO | | NULL | |
+-------------------+------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
Goal
To return a LIST of filtercategories ordered by position, the left-joined tags should be ordered by position as well.
So far trying smth like:
SELECT
fc.*,
GROUP_CONCAT(t.name) AS tagNames
FROM filtercategories fc
LEFT JOIN (filtercategories_tags fc_t, tags t)
ON (
fc_t.filtercategory_id = fc.id AND
t.id = fc_t.tag_id
)
GROUP BY fc.id
ORDER BY fc.position
Problem is that MySQL would not allow to use ORDER BY fc_t.position:
ER_WRONG_FIELD_WITH_GROUP: Expression #1 of ORDER BY clause is not in GROUP BY clause and contains nonaggregated column 'foo_db.fc_t.position' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

Answer 1

the left-joined tags should be ordered by position as well.
Then you should use an ORDER BY clause within GROUP_CONCAT():
SELECT
fc.*,
GROUP_CONCAT(t.name ORDER BY fc_t.position) AS tagNames
FROM filtercategories fc
LEFT JOIN filtercategories_tags fc_t ON fc_t.filtercategory_id = fc.id
LEFT JOIN tags t ON t.id = fc_t.tag_id
GROUP BY fc.id
ORDER BY fc.position
I also fixed your JOIN syntax. Please don't mix explicit JOINs with comma joins in one query. This is hard to understand and debug.