MySQL笔记-group by和聚合函数的使用

Posted 2022-03-22 IT1995

group by：其实就是分组，把同类的组，数据放到一起，然后用聚合函数去统计。下面是详细的说明。

对应的SQL如下：

SELECT * FROM fund_earning_2022 ORDER BY create_time DESC

如下数据内容：

这里用2个域来测试下：

SELECT create_time, day_growth FROM fund_earning_2022 ORDER BY create_time DESC

如果用这样的SQL语句：

SELECT create_time, day_growth FROM fund_earning_2022 GROUP BY create_time ORDER BY create_time DESC

 会报这样的错：

1 queries executed, 0 success, 1 errors, 0 warnings

查询：SELECT create_time, day_growth FROM fund_earning_2022 group by create_time order by create_time desc LIMIT 0, 1000

错误代码： 1055
Expression #2 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'financial.fund_earning_2022.day_growth' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

执行耗时   : 0 sec
传送时间   : 0 sec
总耗时      : 0 sec

原有其实是这条语句对应的表可以理解成这样的。

create_time	day_growth
2022-2-15	0 0.0138735
2022-2-14	0.000195484 -0.0254191
2022-2-11	-0.0000977326 -0.0242744

这里因为数据库操作的原子性，一列不能有两个数据，所以才会有错误提示的。

这里就要用到聚合函数了，如sum(day_growth)就不会报错了。如下SQL语句：

SELECT create_time, SUM(day_growth) FROM fund_earning_2022 GROUP BY create_time ORDER BY create_time DESC