小编典典

数据库查询:如何计算几列的最大值

sql

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

我想得到的是最大的成人人数(此处为2个)和最大的孩子人数(此处为2个)。有没有一种方法可以通过单个查询来实现?感谢您的任何提示。


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2021-05-30

共1个答案

小编典典

使用派生表获取计数,然后选择最大值:

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
2021-05-30