最近把mysql 升级到了5.7.18 然后就发现了一个很明显的变化， ONLY_FULL_GROUP_BY 这个mysql mode 被加了进来， 按照sql 99 的标准这是好事.
但是实际上， mysql 的这个版本只能说almost identical or very close to, 不能说完全相等
简单的说，就是
That is, MySQL 5.7.5m15 will by default reject only those GROUP BY-queries that include non-aggregated expressions in the SELECT-list that are not functionally dependent upon the GROUP BY-list. This not only means that you cannot mess up your GROUP BY-queries anymore (as MySQL will now reject an improper GROUP BY query), it will also not require you to write non-sensical "dummy" aggregates over expressions that can only have one value per aggregated result row. Hurrah!
详细的解释请看这篇文章:
http://rpbouman.blogspot.nl/2014/09/mysql-575-group-by-respects-functional.html