Grouping sales revenue by region and by quarter in SQL

Question

I have a SQL Server with sales_revenue, region, and Year_Quarters. I want to create a table that shows sales_revenue per region by quarter.

Desired output would like something like this:

sales_revenue	region	Quarter_Year
250	Midwest	2015-Q1
150	Northeast	2015-Q1
100	South	2015-Q1

So far, I have tried the following, which has only yielded me sales revenue for each region by day, and simply tells me the quarter of the year that the day falls under.

SELECT
    sales_revenue,
    region,
    CASE
        WHEN MONTH(date_of_sale) BETWEEN 01  AND 03  THEN convert(char(4), YEAR(date_of_sale)) + '-Q1'
        WHEN MONTH(date_of_sale) BETWEEN 04  AND 06  THEN convert(char(4), YEAR(date_of_sale)) + '-Q2'
        WHEN MONTH(date_of_sale) BETWEEN 07  AND 09  THEN convert(char(4), YEAR(date_of_sale)) + '-Q3'
        WHEN MONTH(date_of_sale) BETWEEN 10 AND 12 THEN convert(char(4), YEAR(date_of_sale)) + '-Q4'
    END AS Year_Quarter
FROM dbo.Data$
GROUP BY region, date_of_sale, sales_revenue
ORDER BY Year_Quarter;

Output of the above:

sales_revenue	region	Quarter_Year
200	Midwest	2015-Q1
210	Midwest	2015-Q1
220	Midwest	2015-Q1
190	Midwest	2015-Q1