GROUP BY handler doesn't support operations on aggregate functions when projecting columns.

MariaDB [cs]> describe cs1;

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

| Field | Type    | Null | Key | Default | Extra |

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

| i     | int(11) | YES  |     | NULL    |       |

| it    | int(11) | YES  |     | NULL    |       |

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

2 rows in set (0.00 sec)

MariaDB [cs]> select * from cs1;

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

| i    | it   |

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

|    1 |    2 |

|    3 |    4 |

|   25 |   26 |

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

3 rows in set (0.01 sec)

select sum(i)+1 from cs1;

select concat('1',sum(i)) from cs1;

select not(sum(i)) from cs1;