Question

我一直在努力处理多重计数声明。我的表是这样构建的;

person1, person2, relation
peter     ann      coworkers

我需要计算彼得在恋人之下有多少关系。等等

我想出了这个;

select(
select count(*)
from rel
where person1 = 'peter' and relation = 'coworker'
)as PetersFriends,(
select count(*)
from rel
where person1 = 'peter' and relation = 'lovers'
)
as PetersLovers
;

但我似乎无法让它发挥作用。

Answer 1

select relation, count(*) as RelationCount
from rel
where person1='peter'
group by relation

Answer 2

您的原始查询似乎需要一个透视结果。如果是这种情况，你需要类似的东西。

select person1,
       COUNT(case when relation = 'coworker' then 1 end) AS Friends,
       COUNT(case when relation = 'lovers' then 1 end) AS Lovers
from rel
where person1 IN ('peter','ann','wendy')
GROUP BY person1

Answer 3

假设

Peter, Ann, Coworker

还会有相应的条目：

Ann, Peter, Coworker

然后你可以这样做：

SELECT Person1, Relation, COUNT(1)
FROM Rel
GROUP BY Person1, Relation

否则，你可以这样做：

SELECT Person1, Relation, COUNT(1)
FROM Rel
GROUP BY Person1, Relation
UNION 
SELECT Person2, Relation, COUNT(1)
FROM Rel
GROUP BY Person2, Relation

在SQL中使用多个count语句苦苦挣扎

3 个答案: