数据库多表连接查询中使用group by分组语句，Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'XXX' which is not functionally dependent on columns in GROUP BY claus
需求描述：
要是用两表联合查询，并对查询的结果进行分组：sql如下：
1 SELECT 2 a.`id`, 3 a.`fr_num`, 4 b.`ent_status` 5 FROM 6 `table1` a 7 LEFT JOIN `table2` b 8 ON b.`fr_id` = a.`id` 9 GROUP BY b.`fr_num`
这样的sql语句会报错结果如下：
Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'a.id' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by.
问题处理：
首先了解一下sql的group by的用法：
1、select后面的查询字段要么在group by后，要么是聚合函数
2、如果有条件对结果进行筛选，有两种方式：(1) 先使用where + 条件，然后使用group by (2) 先使用group by，然后使用having进行结果筛选
解决：结合group by 的使用方法对sql进行改进就ok了~
