sql语句怎么实现聚集函数嵌套

有时辰我们在写sql语句的时辰，想实现堆积函数嵌套，怎么实现呢，下面来分享一下方式

东西/原料

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第一步我们在写sql语句的时辰，写sum(min(a))这种函数嵌套格局会呈现语法错误，下面以test表为例，来实现堆积函数嵌套，如下图所示：
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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，如许就实现了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，并求出每组的最年夜值和最小值之差，对所有组的差值进行乞降，如下图所示：
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第三步运行sql语句，我们可以看到成果为38，张三的最年夜最小差值为34，李四的为4，王五的为0，加起来成果准确，如下图所示：
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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，计较每组最年夜值和最小值之差的平均值，成果为12.6667，如下图所示：
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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，计较分了几组，如下图所示：
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第六步输入“select avg(diff) from (SELECT max(second) as diff from test GROUP BY name) as a”语句，计较每组的最年夜值平均值，如下图所示：