Intermittent only_full_group_by errors in AWS Aurora MySQL cluster db
If only_full_group_by is enabled
All Columns of a SELECT must be in the GROUP BY or use a aggregation function
so simply a is in the GROUP BY and b uses an aggregation function
SELECT
 a, MIN(b)
FROM
 mytable
GROUP BY a

So you have now to check all queries with GROUP BY and &quot;correct&quot; them.
see also the manual
Try all queries, if they give the correct answer, that will cost some time.