MySql 的 ONLY_FULL_GROUP_BY

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

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