sql_ mode=only_ full_ group_ By's pit

One 、 Translate a paragraph , English is not good , Forgive me

Syntax error or access violation: 1055 Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'a16.a.id' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

Syntax： grammar .violation： It is illegal to .Expression： expression . clause： clause .contains： contain .nonaggregated： Non aggregation .functionally： Functionality .dependent： rely on .incompatible： Are not compatible

Two 、only_full_group_by：

1、 This rule requires ： Where there are group by The fields that appear later , Must be at the same time select Behind the ; Where there are select Later on 、 Fields that do not appear in the aggregate function at the same time , Must appear at the same time group by Back ”, Check sql Compliance with the above rules .

2、order by The following columns must be in select There is something behind it

3、select、having or order by The following non aggregate columns must all be in group by in

https://zhuanlan.zhihu.com/p/103283746

3、 ... and 、 Aggregate functions （ Combinatorial function ）： Aggregate functions aggregation function Also called group function .  By default The aggregate function will count the current table as a group .https://www.cnblogs.com/xuchuankun/p/9483765.html

Four 、GROUP BY sentence ：GROUP BY Statements are used to combine aggregate functions , Group result sets according to one or more columns .

5、 ... and 、group by Detailed explanation ：https://blog.csdn.net/jerrytomcat/article/details/82351605

https://blog.csdn.net/s00229295/article/details/96041555

6、 ... and 、Having And Where The difference between
where Clause is used before grouping query results , Will not meet where The line of the condition is removed , Filtering data before grouping ,where A condition cannot contain a grouper function , Use where Conditions filter out specific lines .
having Clause is used to filter groups that meet the conditions , Filtering data after grouping , Conditions often include groupings , Use having Conditions filter out specific groups , You can also use multiple grouping criteria for grouping .

7、 ... and 、MYSQL in GROUP BY Do not include all non aggregated fields :https://blog.csdn.net/liufei198613/article/details/82979034

8、 ... and 、 Multi table queries do not seem to follow the above rules ： The following code does not report an error , What's the reason ？

$map['a.user_id'] = $this->auth->id;
        $map['b.type'] = 1;
        $map['b.deletetime'] = null;
        $map['b.endtime'] = ['>', time()];
        $map['b.starttime'] = ['<', time()];
        $field = 'a.id, a.plan_id, b.plan_name, b.times, b.hours, b.endtime, b.starttime,b.type,b.exam_id,c.exam_name, max(d.lasttime) as lasttime';
        $plans = $this->model
            ->alias('a')
            ->where($map)
            ->field($field)
            ->join('__KAOSHI_PLAN__ b', 'a.plan_id = b.id')
            ->join('__KAOSHI_EXAMS__ c', 'b.exam_id = c.id')
            ->join('__KAOSHI_USER_EXAMS__ d', 'a.id = d.user_plan_id', 'left')
            ->group('a.id, b.id')
            ->select();