Question

我在PostgreSQL中有一个表，其中包含我所在国家/地区的人口统计数据。

df.loc[1]

如您所见，每个专业都重复使用Province_names。那么，如何才能使省名不再重复，而只能在单独的栏中获得专业名称？

Answer 1

听起来好像您想旋转表（真的：最好在问题中显示数据和期望的输出！）

demo:db<>fiddle

这是PostgreSQL自9.4起使用FILTER子句的方式

SELECT
    province,
    SUM(people) FILTER (WHERE profession = 'teacher') AS teacher,
    SUM(people) FILTER (WHERE profession = 'banker') AS banker,
    SUM(people) FILTER (WHERE profession = 'supervillian') AS supervillian
FROM mytable
GROUP BY province

如果您想采用更通用的方法，则可以使用CASE子句

SELECT
    province,
    SUM(CASE WHEN profession = 'teacher' THEN people ELSE 0 END) AS teacher,
    SUM(CASE WHEN profession = 'banker' THEN people ELSE 0 END) AS banker,
    SUM(CASE WHEN profession = 'supervillian' THEN people ELSE 0 END) AS supervillian
FROM mytable
GROUP BY province

Answer 2

您想要做的是一个枢轴，在Postgresql中要比在其他rdbms中复杂一些。您可以使用交叉表功能。在此处找到介绍：https://www.vertabelo.com/blog/technical-articles/creating-pivot-tables-in-postgresql-using-the-crosstab-function

对您来说，它看起来像这样：

SELECT * 
FROM crosstab( 'select Province_name, professions, Number_of_people from table1 order by 1,2') 
     AS final_result(Province_name TEXT, data_scientist NUMERIC,data_engineer NUMERIC,data_architect NUMERIC,student NUMERIC);

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2 个答案: