LEFT JOIN not keeping only records that occur in a SELECT query - sql

Question

I have the following SQL select statement that I use to get a subset of products, or wines:
SELECT pv.SkProdVariantId AS id,
pa.Colour AS colour,
FROM Dim.ProductVariant AS pv
JOIN ProductAttributes_new AS pa
ON pv.SkProdVariantId = pa.SkProdVariantId
WHERE pv.ProdTypeName = 'Wines'
The length of this table generated is 3,905. I want to get all the transactional data for these products.
At the moment I'm using this select statement
SELECT c.CalDate AS timestamp,
f.SkProductVariantId AS sku_id,
f.Quantity AS quantity
FROM fact.FTransactions AS f
LEFT JOIN Dim.Calendar AS c
ON f.SkDateId = c.SkDateId
LEFT JOIN (
SELECT pv.SkProdVariantId AS id,
pa.Colour AS colour,
FROM Dim.ProductVariant AS pv
JOIN ProductAttributes_new AS pa
ON pv.SkProdVariantId = pa.SkProdVariantId
WHERE pv.ProdTypeName = 'Wines'
) AS s
ON s.id = f.SkProductVariantId
WHERE c.CalDate LIKE '%2019%'
The calendar dates are correct, but the number of unique products returned is 5,648, rather than the expected 3,905 from the select query.
Why does my LEFT JOIN on the first select query not work as I expect it to, please?
Thanks for any help!

Answer 1

If you want all the rows form your query, it needs to be the first reference in the LEFT JOIN. Then, I am guessing that you want transaction in 2019:
select . . .
from (SELECT pv.SkProdVariantId AS id, pa.Colour AS colour,
FROM Dim.ProductVariant pv JOIN
ProductAttributes_new pa
ON pv.SkProdVariantId = pa.SkProdVariantId
WHERE pv.ProdTypeName = 'Wines'
) s LEFT JOIN
(fact.FTransactions f JOIN
Dim.Calendar c
ON f.SkDateId = c.SkDateId AND
c.CalDate >= '2019-01-01' AND
c.CalDate < '2020-01-01'
)
ON s.id = f.SkProductVariantId;
Note that this assumes that CalDate is really a date and not a string. LIKE should only be used on strings.

Answer 2

You misunderstand somehow how outer joins work. See Gordon's answer and my request comment on that.
As to the task: It seems you want to select transactions of 2019, but you want to restrict your results to wine products. We typically restrict query results in the WHERE clause. You can use IN or EXISTS for that.
SELECT
c.CalDate AS timestamp,
f.SkProductVariantId AS sku_id,
f.Quantity AS quantity
FROM fact.FTransactions AS f
INNER JOIN Dim.Calendar AS c ON f.SkDateId = c.SkDateId
WHERE DATEPART(YEAR, c.CalDate) = 2019
AND f.SkProductVariantId IN
(
SELECT pv.SkProdVariantId
FROM Dim.ProductVariant AS pv
WHERE pv.ProdTypeName = 'Wines'
);
(I've removed the join to ProductAttributes_new, because it doesn't seem to play any part in this query.)