Sub-query with GROUP BY and ORDER BY allows non-aggregates in projection.

MariaDB [test]> select * from ( select count(1), i, i2 from cs1 group by i order by i2 ) a;

+----------+------+------+

| count(1) | i    | i2   |

+----------+------+------+

|        1 |    1 |   36 |

|        1 |  100 |    5 |

|        1 |   26 |    1 |

|        1 |   25 |  103 |

|        1 |    1 |   41 |

|        1 |    2 |   42 |

+----------+------+------+

6 rows in set (0.028 sec)

MariaDB [test]> select * from ( select count(1), i, i2 from cs1 group by i order by i2 )a ;

ERROR 1815 (HY000): Internal error: IDB-2021: 'i2' is not in GROUP BY clause. All non-aggregate columns in the SELECT and ORDER BY clause must be included in the GROUP BY clause.