Prior to 5.7, MySQL always accepted non-aggregated fields. Version 5.7 introduced ONLY_FULL_GROUP_BY, but since that change broke lots of code that depended on

Prior to 5.7, MySQL always accepted non-aggregated fields. Version 5.7 introduced ONLY_FULL_GROUP_BY, but since that change broke lots of code that depended on this historical behavior, many people disabled it.