Removal of implicit and explicit sorting for GROUP BY

Removal of implicit and explicit sorting for GROUP BY

In MySQL, historically GROUP BY was used to provide sorting as well. If a query specified GROUP BY, the result was sorted as if ORDER BY was present in the query.

mysql-5.7> CREATE TABLE t (id INTEGER,  cnt INTEGER);
Query OK, 0 rows affected (0.03 sec)

mysql-5.7> INSERT INTO t VALUES (4,1),(3,2),(1,4),(2,2),(1,1),(1,5),(2,6),(2,1),(1,3),(3,4),(4,5),(3,6);
Query OK, 12 rows affected (0.02 sec)
Records: 12  Duplicates: 0  Warnings: 0

mysql-5.7> SELECT id, SUM(cnt) FROM t GROUP BY id;
+------+----------+
| id   | SUM(cnt) |
+------+----------+
|    1 |       13 |
|    2 |        9 |
|    3 |       12 |
|    4 |        6 |
+------+----------+
4 rows in set (0.00 sec)

MySQL here implicitly sorts the results from GROUP BY (i.e.…

Source: Removal of implicit and explicit sorting for GROUP BY