Group by Month and Year in SQL - sql

Question

I am trying to make a query, I must receive a date and give a report in which I must show the sum of the amounts at the end of a month.
What I have so far is this:
CREATE PROCEDURE consulta
#fecha DATE
AS
SELECT
SUM(dca.UNIDADES) as Amount,
MONTH(ca.FINICIO) as Month,
YEAR(ca.FINICIO)
FROM
DETALLE_CONTRATO_ALQUILER dca
INNER JOIN
CONTRATOALQUILER ca ON dca.CODCONTRATO = ca.CODCONTRATO
AND ca.FINICIO >= #fecha
AND YEAR(ca.FINICIO) = YEAR(#fecha)
GROUP BY
MONTH(ca.FINICIO), YEAR(ca.FINICIO)
HAVING
SUM(dca.UNIDADES) > 2;
The comparison of years is because I only have to obtain the months of that same year.
I also attach my diagram:
The context of the database is about product rentals, the tables I use are the rental contract and the detail
I know I get errors because when I enter a specific date, I do not get results. I do not know what I'm failing. My query is correctly logical?
What I expect to obtain is:
Amount | Month | Year
12 1 2017
45 2 2017
...
Here's the example

Answer 1

I would assume all rows of both tables have matching row(s) in the other table, so an INNER JOIN is what you need.
There's a small detail in your query that smells fishy. Your join includes filtering conditions that may throw rows out of the query. Maybe you should place the filtering conditions in a WHERE clause instead of a JOIN clause, as in:
SELECT
SUM(dca.UNIDADES) as Amount,
MONTH(ca.FINICIO) as Month,
YEAR(ca.FINICIO)
FROM
DETALLE_CONTRATO_ALQUILER dca
INNER JOIN
CONTRATOALQUILER ca ON dca.CODCONTRATO = ca.CODCONTRATO
WHERE ca.FINICIO >= #fecha -- Using WHERE instead of JOIN here!
AND YEAR(ca.FINICIO) = YEAR(#fecha)
GROUP BY
MONTH(ca.FINICIO), YEAR(ca.FINICIO)
HAVING
SUM(dca.UNIDADES) > 2;
You can place filtering in the JOIN clause and that is very useful for OUTER JOINs. However, for INNER JOINs that applies to the join itself and may filter out rows you wanted to include.