MySQL如何将平均值取到特定范围内 [英] MySQL how to get avg of values into specific range

问题描述

我有以下表格数据:

value
1
5
10.5
12
36

我想将这些值映射到:

range      avg
0-21       (1 + 5 + 10.5 + 12) / 4
21.001-34  0
34.001-64  36
64 +       0

基本上将每个值映射到范围，并计算每个范围内所有值的平均值.

Basically map each value to ranges and calculate the avg of all values in each range.

我试图做:

select 
case
when avggeneral between 0 and 21 then ' 0-21'
when avggeneral between 21.00001 and 34 then ' 21-34'
when avggeneral between 34.00001 and 64 then ' 34-64'
else '64+'
end as 'range',
AVG(*) as 'avg'
from table

但这不起作用...我不知道如何制作静态范围...

but this doesn't work... I don't know how to make the static ranges...

如何在MySQL中做到这一点?

How can I do that in MySQL?

方法应为: 1.将值映射到这些组中(0-21、21-34等.) 2.计算每组的AVG.

Methology should be: 1. Map values into these groups ( 0-21, 21-34 etc..) 2. calulate AVG in each group.

上面示例的期望输出是这样的:

Desired output for above example is this:

range      avg
0-21       7.125
21.001-34  0
34.001-64  36
64 +       0

range列是静态的.始终带有5行. avg列是动态的.值是value列的实际AVG.

The range column is static. Always with 5 rows. The avg column is dynamic.. the values there are the actual AVGs of value column.

推荐答案

您可以使用UNION ALL和LEFT JOIN与其建立范围列表:

You could build a list of ranges using UNION ALL and LEFT JOIN with it:

SELECT CONCAT(IFNULL(ranges.min, '∞'), '-', IFNULL(ranges.max, '∞')) AS `range`, avg(value) AS avg
FROM (
    SELECT 0 AS min, 21 AS max UNION ALL
    SELECT 21, 34 UNION ALL
    SELECT 34, 64 UNION ALL
    SELECT 64, NULL
) AS ranges
LEFT JOIN t ON (ranges.min IS NULL OR value >= ranges.min) AND
               (ranges.max IS NULL OR value <  ranges.max)
GROUP BY ranges.min, ranges.max

请注意，上述查询会将20.9999放在[0-21)范围内，而21.0000放在[21-34)范围内.

Note that the above query will put 20.9999 inside [0-21) and 21.0000 inside [21-34) range.

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