按多列分組：SQL

Question

我有一張桌子：

我有一個查詢給了我

我想要這樣的東西：

用於上述結果的查詢是：

select ucountry,sum(Males) Males,sum(females ) Females from (
                                                  select ucountry,
                                                         case when gender = 'M' then count(1) else 0 end as Males,
                                                         case when gender = 'F' then count(1) else 0 end as females
                                                  from testing.test_users
                                                  group by ucountry, gender
                                              ) a group by ucountry;

我絕對不是在這里做最好的事情。 大家覺得有什么更好的嗎？

Answer 1

如果您要計算每個國家/地區的男性和女性人數：

select ucountry,
sum(case when gender = 'M' then 1 else 0 end) as males,
sum(case when gender = 'F' then 1 else 0 end) as females
from testing.test_users
group by ucountry

Answer 2

如果您使用的是PostgreSQL那么您也可以使用FILTER

select ucountry, COUNT(*) FILTER (WHERE gender = 'M') males, 
COUNT(*) FILTER (WHERE gender = 'F') females from testing.test_users group by ucountry

Answer 3

您應該僅在ucountry列上應用GROUP BY 。 使用以下查詢在SQL 服務器中獲得預期結果：

SELECT  
    ucountry, 
    SUM(IIF(Name = 'M', 1, 0)) males,
    SUM(IIF(Name = 'F', 1, 0)) females
FROM testing.test_users
GROUP BY ucountry