SQL GROUP BY before JOIN - sequence when querying

SQL GROUP BY before JOIN - sequence when querying

SELECT
Income.point, Income.date, SUM(out), SUM(inc)
FROM
Income
LEFT JOIN
Outcome ON Income.point = Outcome.point
AND Income.date = Outcome.date
GROUP BY
Income.point, Income.date
UNION
SELECT
Outcome.point, Outcome.date, SUM(out), SUM(inc)
FROM
Outcome
LEFT JOIN
Income ON Income.point = Outcome.point
AND Income.date = Outcome.date
GROUP BY
Outcome.point, Outcome.date;
I have this code what I want to do is to group by before joining. I can't
find a solution on google so will you please explain what to change in
queries to change sequence.
By the way this is exercise 30 from http://www.sql-ex.ru/, which says:
Under the assumption that the income (inc) and expenses (out) of the money
at each outlet (point) are registered any number of times a day, get a
result set with fields: outlet, date, expense, income.
Note that a single record must correspond to each outlet at each date.
Use Income and Outcome tables.