How to aggregate using distinct values across two columns? - sql

Question

I have the following data in an orders table:
revenue expenses location_1 location_2
3 6 London New York
6 11 Paris Toronto
1 8 Houston Sydney
1 4 Chicago Los Angeles
2 5 New York London
7 11 New York Boston
4 6 Toronto Paris
5 11 Toronto New York
1 2 Los Angeles London
0 0 Mexico City London
I would like to create a result set that has 3 columns:
a list of the 10 DISTINCT city names
the sum of revenue for each city
the sum of expenses for each city
The desired result is:
location revenue expenses
London 6 13
New York 17 33
Paris 10 17
Toronto 15 28
Houston 1 8
Sydney 1 8
Chicago 1 4
Los Angeles 2 6
Boston 7 11
Mexico City 0 0
Is it possible to aggregate on distinct values across two columns? If yes, how would I do it?
Here is a fiddle:
http://sqlfiddle.com/#!9/0b1105/1

Answer 1

Shorter (and often faster):
SELECT location, sum(revenue) AS rev, sum(expenses) AS exp
FROM (
SELECT location_1 AS location, revenue, expenses FROM orders
UNION ALL
SELECT location_2 , revenue, expenses FROM orders
) sub
GROUP BY 1;
May be faster:
WITH cte AS (
SELECT location_1, location_2, revenue AS rev, expenses AS exp
FROM orders
)
SELECT location, sum(rev) AS rev, sum(exp) AS exp
FROM (
SELECT location_1 AS location, rev, exp FROM cte
UNION ALL
SELECT location_2 , rev, exp FROM cte
) sub
GROUP BY 1;
The (materialized!) CTE adds overhead, which may outweigh the benefit. Depends on many factors like total table size, available indexes, possible bloat, available RAM, storage speed, Postgres version, ...
fiddle

Answer 2

You could UNION ALL two queries and then select from it...
select location, sum(rev) as rev, sum(exp) as exp
from (
select location_1 as location, sum(revenue) as rev, sum(expenses) as exp
from orders
group by location_1
union all
select location_2 as location, sum(revenue) as rev, sum(expenses) as exp
from orders
group by location_2
)z
group by location
order by 1