TSQL group by generate duplicate row - sql-server

Question

I'm trying to extract all prices and taxes by dates range (not necessary the same date) in 2 column and group by ID.
Because I need to group by 2 others columns because T-SQL need that:
Column '...' is invalid in the select list because
it is not contained in either an aggregate function or the GROUP BY clause.
I have a duplicate user/ID sometimes. ( don't know why by the way..)
I have this SQL:
WITH myQuery AS
(
Select
c.name, c.id,
CASE
WHEN g.dateCreated BETWEEN CAST ('2016-06-01 00:00:00.000' AS DATETIME)
AND CAST ('2017-05-31 23:59:59.000' AS DATETIME)
THEN SUM(CAST(g.price AS decimal(20,2) ))
ELSE 0
END AS TOTAL_PRICE,
CASE
WHEN g.dateCreated BETWEEN CAST ('2016-01-01 00:00:00.000' AS DATETIME)
AND CAST ('2016-12-31 23:59:59.000' AS DATETIME)
THEN SUM(CAST(g.tax AS decimal(20,2) ))
ELSE 0
END AS TOTAL_TAX
FROM customers c
inner join goodies g
ON c.id = g.customer_id
GROUP BY c.name, c.id, g.dateCreated
)
SELECT count(*) FROM myQuery
I got 5203 rows. I have only 5031 users.
When I Analyse my data, I have some duplicate data.
Example:
Alex, 12, 0.00, 0.00
Alex, 12, 100.00, 14.55
Nancy, 4, 0.00, 0.00
Arthur, 97, 48.14, 09.17
I tried to group by only by id but it seem that I can't do that.
Why I have a duplicate data and How to prevent that and ensure that I have 1 row by USER even if they don't buy goodies?

Answer 1

Correcting your conditional aggregation and removing dateCreated from the group by:
with myQuery as (
select
c.name
, c.id
, total_price = sum(case
when g.dateCreated >= '20160601' and g.dateCreated < '20170601'
then cast(g.price as decimal(20,2))
else 0
end)
, total_tax = sum(case
when g.dateCreated >= '20160101' and g.dateCreated < '20170101'
then cast(g.tax as decimal(20,2))
else 0
end)
from customers c
left join goodies g
on c.id = g.customer_id
group by
c.name
, c.id
--, g.dateCreated
)
select count(*) from myQuery;
Changing the inner join to a left join will return customers even if they have no corresponding row in goodies.
I also changed your date range code to be more explicit about what is included.
Reference:
Bad habits to kick : mis-handling date / range queries - Aaron Bertrand
What do between and the devil have in common? - Aaron Bertrand