> SELECT .. FOR UPDATE?:
>
> https://www.postgresql.org/docs/10/static/sql-select.html#SQL-FOR-UPDATE-SHARE
>
>
> https://www.postgresql.org/docs/10/static/explicit-locking.html#LOCKING-ROWS
>
It says: "Currently, FOR NO KEY UPDATE, FOR UPDATE, FOR SHARE and FOR
KEY SHARE cannot be specified with GROUP BY."
Regards,
Vitaliy