PostgreSQL根据两个变量计算面积比例答案

【问题标题】：PostgreSQL calculate area proportion based on two variablesPostgreSQL根据两个变量计算面积比例
【发布时间】：2021-02-25 15:34:17
【问题描述】：

我对 PostgreSQL 比较陌生，无法真正解决一个简单的问题。以简化表为例：

create table example(
    objectid integer,
    soil_type integer,
    area double precision);
    values (2,4,23.5),
    (2,3,30.45),
    (2,6,20.1),
    (1,3,10.5),
    (3,6,40.5),
    (3,4,20);

如何计算每个对象 id 中每种土壤类型的面积份额？

【问题讨论】：

标签： postgresql area

【解决方案1】：

您需要每个 obectid 的面积总和。 - 但同时保留所有行。这是通过窗口函数完成的：sum(area) OVER(PARTITION BY objectid)。
- 或者，如果您需要每个土壤类型的每个 objectid 的份额，PARTITION BY soil_type。

SELECT 
objectid, 
soil_type,
area, 
area / sum(area) OVER(PARTITION BY objectid) AS share 
FROM example 
ORDER BY 1,2;

输出：

 objectid | soil_type | area  |        share        
----------+-----------+-------+---------------------
        1 |         3 |  10.5 |                   1
        2 |         3 | 30.45 | 0.41120864280891284
        2 |         4 |  23.5 | 0.31735313977042534
        2 |         6 |  20.1 |  0.2714382174206617
        3 |         4 |    20 |  0.3305785123966942
        3 |         6 |  40.5 |  0.6694214876033058

或者：

SELECT 
objectid, 
soil_type,
area, 
area / sum(area) OVER(PARTITION BY soil_type) AS share 
FROM example 
ORDER BY 1,2;

输出：

 objectid | soil_type | area  |        share        
----------+-----------+-------+---------------------
        1 |         3 |  10.5 |  0.2564102564102564
        2 |         3 | 30.45 |  0.7435897435897435
        2 |         4 |  23.5 |  0.5402298850574713
        2 |         6 |  20.1 |  0.3316831683168317
        3 |         4 |    20 | 0.45977011494252873
        3 |         6 |  40.5 |  0.6683168316831684
(6 rows)

【讨论】：

【解决方案2】：

这会按土壤类型进行简单的分组以获得每个土壤类型的总和（面积），并将其放入子查询中，然后计算总和以获得总面积：

select soil_type, area, area / sum(area) over () as proportion 
from (select soil_type, sum(area) area from example group by soil_type)x;

 soil_type | area  |     proportion
-----------+-------+---------------------
         3 | 40.95 |  0.2823164426059979
         4 |  43.5 | 0.29989658738366076
         6 |  60.6 | 0.41778697001034126

你也可以这样做：

with x as (select soil_type, sum(area) area from example group by soil_type)
select soil_type, area, area / (SELECT sum(area) FROM x) as proportion from x;

【讨论】：