I have an idea/request for enhancement to PostgreSQL (I'm new to PostgreSQL and this mailing list).
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Idea:
There's a technique in Oracle SQL that can be used to simplify aggregation queries:
Aggregate on a particular column, but get information from a different column, using a simple calculated column in the SELECT list.
--Oracle
--For a given country, what city has the highest population? (where the country has more than one city)
--Include the city name as a column.
select
country,
count(*),
max(population),
max(city) keep (dense_rank first order by population desc)
from
cities
group by
country
having
count(*) > 1
As shown above, the following calculated column can bring in the city name, even though the city name isn't in the GROUP BY:
max(city) keep (dense_rank first order by population desc)
There are a number of ways to achieve that kind of thing using PostgreSQL. I want a solution that lets me do it in a calculated column -- all within a single SELECT query (no subqueries, joins, WITH, etc.).