假设我有下表
claim_date person_type
------------------------
01-01-2012 adult
05-05-2012 adult
12-12-2012 adult
12-12-2012 adult
05-05-2012 child
05-05-2012 child
12-12-2012 child
当我执行以下查询时:
select
claim_date,
sum(case when person_type = 'adult' then 1 else 0 end) as "nbr_of_adults",
sum(case when person_type = 'child' then 1 else 0 end) as "nbr_of_children"
from my_table
group by claim_date
;
我在这里得到这个结果:
claim_date nbr_of_adults nbr_of_children
---------------------------------------------
01-01-2012 1 0
05-05-2012 1 2
12-12-2012 2 1
我希望收到的是最大成人人数(此处:2人)和最多儿童人数(此处:2人)。 有没有办法通过单个查询实现这一目标?感谢任何提示。
答案 0 :(得分:3)
使用派生表获取计数,然后选择max:
select max(nbr_of_adults) max_adults,
max(nbr_of_children) max_children
from
(
select
sum(case when person_type = 'adult' then 1 else 0 end) as "nbr_of_adults",
sum(case when person_type = 'child' then 1 else 0 end) as "nbr_of_children"
from my_table
group by claim_date
) a
答案 1 :(得分:2)
使用嵌套查询:
select max(nbr_of_adults) maxAd, max(nbr_of_children), maxCh from
(
select
claim_date,
sum(case when person_type = 'adult' then 1 else 0 end) as "nbr_of_adults",
sum(case when person_type = 'child' then 1 else 0 end) as "nbr_of_children"
from my_table
group by claim_date
)
答案 2 :(得分:2)
我不知道你的dbms是什么,但是在sybase上它可以工作:
select
max(sum(case when person_type = 'adult' then 1 else 0 end)) as "nbr_of_adults",
max(sum(case when person_type = 'child' then 1 else 0 end)) as "nbr_of_children"
from my_table
group by claim_date
答案 3 :(得分:0)
select
person_type,
sum(case when person_type = 'adult' then 1 else 0 end) as "nbr_of_adults",
sum(case when person_type = 'child' then 1 else 0 end) as "nbr_of_children"
from my_table
group by claim_date ;
答案 4 :(得分:0)
如果您的SQL产品支持窗口聚合函数,您可以尝试这样的事情:
SELECT DISTINCT
MAX(COUNT(CASE person_type WHEN 'adult' THEN 1 END)) OVER () AS max_adult_count,
MAX(COUNT(CASE person_type WHEN 'child' THEN 1 END)) OVER () AS max_child_count
FROM claim_table
GROUP BY claim_date
我还用条件COUNT替换了你的条件SUM,这在我看来更清晰,更简洁。