DB query: How to count maximum for several columns - sql

Question

Assume I have the following table
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
When I execute the following query:
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
;
I get this result here:
claim_date nbr_of_adults nbr_of_children
---------------------------------------------
01-01-2012 1 0
05-05-2012 1 2
12-12-2012 2 1
What I would like to receive is the maximum number of adults (here: 2) and the maximum number of children (here: 2).
Is there a way to achieve this with a single query? Thanks for any hints.

Answer 1

Use derived table to get counts, and then select 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

Answer 2

With nested query :
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
)

Answer 3

I don't know what is your dbms, but on sybase it works:
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

Answer 4

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 ;

Answer 5

If your SQL product supports window aggregate functions, you could try something like this:
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
I also replaced your conditional SUM with a conditional COUNT, which seemed to me both clearer and more succinct.