下边sql,执行没有问题，但是因为要查询数据操作需要主键，加上主键就存在问题；
SELECT a.`year`, a.`month`, sum(a.expend_money) aa FROM budget_expend a WHERE a.`year` = 2020 GROUP BY a.`month`;
错误一：
分组没有成功，把month为2的月份都查出来了；
SELECT a.id,a.`year`, a.`month`, sum(a.expend_money) aa FROM budget_expend a WHERE a.`year` = 2020 GROUP BY a.`month`,a.id;
错误二：
此方法报错1055
SELECT a.id,a.`year`, a.`month`, sum(a.expend_money) aa FROM budget_expend a WHERE a.`year` = 2020 GROUP BY a.`month`;
解决方式：
使用 any_value() 函数解决；
SELECT any_value (a.id), a.`year`, a.`month`, sum(a.expend_money) aa FROM budget_expend a WHERE a.`year` = 2020 GROUP BY a.`month`;