Calculate relative errors in Postgres

Question

Is there an easy way to calculate errors in Postgres given a table that looks something like this:

id | bool  | score
1  | False | 9
1  | True  | 9.6
2  | False | 5
2  | True  | 4.7

The output that I want id | (False_row - True_row)/True_row:

id | err
1  | -0.0625
2  | 0.063829

Answer 1

SELECT
    id,
    (false_row - true_row) / true_row
FROM (
    SELECT
        id,
        SUM(CASE WHEN bool THEN score ELSE 0 END) AS true_row,
        SUM(CASE WHEN NOT bool THEN score ELSE 0 END) AS false_row
    FROM
        table_name
    GROUP BY
        id
) AS sub;

In the subquery ( sub ) take the true_row and the false_row . This can be done using a variety of aggregate functions, SUM for example.

When you have your true_row and false_row just do the calculations in the outer query.