postgresql one column 2 opposite criteria - postgresql

Question

In my data set, I am looking for value that have both positive and negative result under the amount category. For example, one entity can be bank account, and there are money coming in (positive number) and money going out (negative number).
SELECT description, account_subtype_id, subcategory_id, (case when amount > 0 then 1 end) AS amount_p, (case when amount < 0 then 0 end) AS amount_n
FROM mx.transactions
LIMIT 100
;
This approach doesn't help much because now my data looks like:
bank_A 1 null
bank_A null 0
But I really want to get something like:
bank_A 1 0
because this will be really helpful for my analysis.
Actually. If there is a way to do this, it would be even better:
For example, an entity has
Bank_A $500 -$300 -- (these two results both are from the amount column)

Answer 1

If you want just one row per description, you need to group by description and use aggregate functions. A clean way to check whether there's any positive or negative amount would be to check whether min(amount) and max(amount) are less/greater than 0:
SELECT
description,
min(amount) < 0 AS amount_n,
max(amount) > 0 AS amount_p
FROM mx.transactions
GROUP BY description
These tests will give you true and false values, but you can use them in your CASE/IF statements if you want something else. Or to get the actual values rather than testing against 0, just use min and max directly.
It looks like you've got multiple columns potentially acting as your bank_A identifier. If that's the case, you can GROUP BY all of them.
SELECT
description,
account_subtype_id,
subcategory_id,
min(amount),
max(amount)
FROM mx.transactions
GROUP BY description, account_subtype_id, subcategory_id