sql语句怎么实现聚集函数嵌套

sql语句怎么实现聚集函数嵌套

有时候我们在写sql语句的时候，想实现聚集函数嵌套，怎么实现呢，下面来分享一下方法

第一步我们在写sql语句的时候，写sum(min(a))这种函数嵌套格式会出现语法错误，下面以test表为例，来实泛哄现聚集函数嵌套，如下图所示：

第二步输入“select sum(diff) from (SELECT max(second)-min(second) as diff from test GROUP BY name) as a”语句，这样就实现了sum函数和max函数、min函数的嵌套，这句sql语句的意思是按name字段进行分组，并求出每组的最大值和最小值之差，对所有组的差值进行求和，如下图所示：

第三步运行sql语句，我们可以看到结果为38，张三的最大最小差值为34，李四的为4，王五的为0，加起来结果正确，如下图所示：

第四步我们也可以输入“select avg(diff) from (SELECT max(second)-min(second) as diff from test GROUP BY name) as a”语句，计算每组最大值和最小值之差的平均值，结果为12.6667，如下图所捧脾虚示：

第五步输入“select count(diff) from (SELECT max(second)-min(second) as diff from test GROUP BY name) as a”语句，计算分了几组，如下图所示：

第六步肺信输入“select avg(diff) from (SELECT max(second) as diff from test GROUP BY name) as a”语句，计算每组的最大值平均值，如下图所示：