Finding Related Items

I was thinking last night of restructuring the way "Related Items" are pulled from the database for one of our sites. Basically at the moment it is upto the client to flag two products as related. I'm thinking of using a new method of tagging the products and then finding related products based on the tags assigned -the general code for this is below but what I want to know is, is using "IN" the most efficient way of doing this?

TIA

Tim


DECLARE @ItemId int
SET @ItemId = 1

SELECT
COUNT(i.ItemId) AS MatchingTags,
i.ItemId,
i.ItemName
FROM
tst_Items i LEFT JOIN txt_x_Items_Tags x
ON i.ItemId = x.ItemId
WHERE
x.TagId IN (
SELECT
t.TagId
FROM
tst_Tags t LEFT JOIN txt_x_Items_Tags x
ON t.TagId = x.TagId
WHERE
x.ItemId = @ItemId
)
GROUP BY
i.ItemId,
i.ItemName
HAVING
i.ItemId <> @ItemId
ORDER BY
MatchingTags DESC


The testing data:

CREATE TABLE [dbo].[tst_Items](
[ItemId] [int] NOT NULL,
[ItemName] [nvarchar](50) NOT NULL
) ON [PRIMARY]
GO
CREATE TABLE [dbo].[tst_Tags](
[TagId] [int] NOT NULL,
[TagName] [nvarchar](50) NOT NULL
) ON [PRIMARY]
GO
CREATE TABLE [dbo].[txt_x_Items_Tags](
[ItemId] [int] NOT NULL,
[TagId] [int] NOT NULL
) ON [PRIMARY]
GO
INSERT INTO tst_Items VALUES (1, 'Test Item 1')
INSERT INTO tst_Items VALUES (2, 'Test Item 2')
INSERT INTO tst_Items VALUES (3, 'Test Item 3')
INSERT INTO tst_Items VALUES (4, 'Test Item 4')

INSERT INTO tst_Tags VALUES (1, 'Tag 1')
INSERT INTO tst_Tags VALUES (2, 'Tag 2')
INSERT INTO tst_Tags VALUES (3, 'Tag 3')
INSERT INTO tst_Tags VALUES (4, 'Tag 4')

INSERT INTO txt_x_Items_Tags VALUES (1, 1)
INSERT INTO txt_x_Items_Tags VALUES (1, 2)
INSERT INTO txt_x_Items_Tags VALUES (1, 3)
INSERT INTO txt_x_Items_Tags VALUES (2, 1)
INSERT INTO txt_x_Items_Tags VALUES (2, 3)
INSERT INTO txt_x_Items_Tags VALUES (3, 1)
INSERT INTO txt_x_Items_Tags VALUES (3, 2)
INSERT INTO txt_x_Items_Tags VALUES (1, 4)
INSERT INTO txt_x_Items_Tags VALUES (4, 4)
GO


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