标量子查询产生多个元素

Question

I know this error has been produced many time and a lot of answers came by but I believe every situation might be unique.

So i am trying to get a deficit value(imports - exports) from a table. Both values are on one column

value account
100  export
200  import

SO now i need to calculate the deficit or surplus, which is either import-export or export-import. I tried scalar subqueries but i am always getting this error.

SELECT label, product_type,status,((select value from Task2.quarterly_report where account="Imports") - (select value from Task2.quarterly_report where account="Exports")) As trade_deficit

so basically i am trying to get a table with:-

label  product_type status trade_deficit

Can anyone explain to me the issue and why is it happening and how to solve it. Thanks in advance

Answer 1

You can use the conditional aggregation:

select sum(case when account = 'import' then value
                when account = 'export' then - value
           end)
from t;

This is based on the question and sample data. I don't see what your query has to do with the rest of the question.