Non aggregated columns not named in GROUP BY clause are accepted in mysql unless only_full_group_by is set.

Finding those queries in application code is hard.

Thus it would be nice when those queries would rise a warning in P_S events_statements_history* tables so they could be found and eliminated before setting sql_mode = 'only_full_group_by'

select a, b, count from test group by a;
OK
select * from performance_schema.events_statements_history where warnings > 0;
-> query should be listed.

List those queries in P_S.events_statements_history* tables.