T-SQL Insert - Select in Table variable is very slow - tsql

Question

I have a table variable and I am inserting in it some values using the "Insert Into - Select" statement. The select is a combination of few joins, and when it is executed separately it takes 3 seconds. The problem is that the whole code takes 3-4 minutes to executed. I wonder is there a particular reason for this.
This is the my table variable declaration:
DECLARE #Result TABLE
(
ProductID NVARCHAR(25) PRIMARY KEY
,ProductName NVARCHAR(100)
,ProductCategoryID TINYINT
,ProductCategory NVARCHAR(50)
,ProductSubCategoryID TINYINT
,ProductSubCategory NVARCHAR(50)
,BrandID TINYINT
,Brand NVARCHAR(50)
)
I have an other table variable which I initialize with some data, and this is its structure:
DECLARE #TempTable TABLE
(
ProtoSurveyID INT,
ProductID NVARCHAR(25) PRIMARY KEY
)
and the following code is my problem statement (insert into - select):
INSERT INTO #Result (ProductID,ProductName,ProductCategoryID,ProductCategory,ProductSubCategoryID,ProductSubCategory,BrandID,Brand)
SELECT
Products.ProductID AS ProductID
,Products.ProductName AS ProductName
,ProductCategories.ProductCategoryID AS ProductCategoryID
,ProductCategories.ProductCategory AS ProductCategory
,ProductSubCategories.ProductSubCategoryID AS ProductSubCategoryID
,ProductSubCategories.ProductSubCategory AS ProductSubCategory
,Brands.BrandID AS BrandID
,Brands.Brand AS Brand
FROM
(
SELECT
CAST(A.Col001 AS tinyint) AS ProductCategoryID
,CAST(A.Col002 AS tinyint) AS BrandID
,CAST(A.Col003 AS nvarchar(25)) AS ProductID
,CAST(A.Col004 AS nvarchar(100)) AS ProductName
,CAST(A.Col006 As tinyint) AS ProductSubCategoryID
,B.ProtoSurveyID
FROM DataSetsMaterializedDataSqlvariant A
INNER JOIN #TempTable B
ON B.ProductID=CAST(A.Col003 AS nvarchar(25))
WHERE DataSetsMaterializedInternalRowsetID = 3
) Products
INNER JOIN
(
SELECT CAST(A.Col001 AS tinyint) AS BrandID
, CAST(A.Col002 AS nvarchar(50)) AS Brand
FROM DataSetsMaterializedDataSqlvariant A
WHERE DataSetsMaterializedInternalRowsetID = 1
)Brands On Products.BrandID=Brands.BrandID
INNER JOIN
(
SELECT CAST(A.Col001 AS tinyint) AS ProductCategoryID
,CAST(A.Col002 AS nvarchar(50)) AS ProductCategory
FROM DataSetsMaterializedDataSqlvariant A
WHERE DataSetsMaterializedInternalRowsetID = 2
) ProductCategories On Products.ProductCategoryID=ProductCategories.ProductCategoryID
INNER JOIN
(
SELECT CAST(A.Col001 AS tinyint) AS ProductSubCategoryID
, CAST(A.Col002 AS nvarchar(50)) AS ProductSubCategory
FROM DataSetsMaterializedDataSqlvariant A
WHERE DataSetsMaterializedInternalRowsetID = 11
) ProductSubCategories on Products.ProductSubCategoryID=ProductSubCategories.ProductSubCategoryID
As I told before, if I comment the insert line the query takes 3 seconds, otherwise - a very long time.
EDIT: Here is my execution plan - most of the cost is table scan, but why it takes so many time when insert is make, and happens to quick without it?
The follow is my new inline function:
CREATE FUNCTION [dbo].[fn_XxCustom_RetailAudits_GetProductsForFilter]
(
#SecurityObjectUserID BIGINT
)
RETURNS TABLE
AS
RETURN
WITH CTE(ProtoSurveyID,ProductID) AS
(
SELECT DISTINCT CAST(B.ProtoSurveyID AS INT)
,CAST(A.Col002 AS NVARCHAR(25)) AS ProductID
FROM DataSetsMaterializedDataSqlvariant A
JOIN SurveyInstances B ON A.Col001=B.SurveyInstanceID AND CAST(B.ProtoSurveyID AS INT) IN (SELECT ProtoSurveyID FROM dbo.fn_Filter_GetProtoSurveysAllowedShort(#SecurityObjectUserID, 'CLIENTACCESS',NULL))
WHERE DataSetsMaterializedInternalRowsetID = 5
)
SELECT
Products.ProductID AS ProductID
,Products.ProductName AS ProductName
,ProductCategories.ProductCategoryID AS ProductCategoryID
,ProductCategories.ProductCategory AS ProductCategory
,ProductSubCategories.ProductSubCategoryID AS ProductSubCategoryID
,ProductSubCategories.ProductSubCategory AS ProductSubCategory
,Brands.BrandID AS BrandID
,Brands.Brand AS Brand
FROM
(
SELECT
CAST(A.Col001 AS tinyint) AS ProductCategoryID
,CAST(A.Col002 AS tinyint) AS BrandID
,CAST(A.Col003 AS nvarchar(25)) AS ProductID
,CAST(A.Col004 AS nvarchar(100)) AS ProductName
,CAST(A.Col006 As tinyint) AS ProductSubCategoryID
,B.ProtoSurveyID
FROM CTE B
INNER JOIN DataSetsMaterializedDataSqlvariant A
ON B.ProductID=CAST(A.Col003 AS nvarchar(25))
WHERE DataSetsMaterializedInternalRowsetID = 3
) Products
INNER JOIN
(
SELECT CAST(A.Col001 AS tinyint) AS BrandID
,CAST(A.Col002 AS nvarchar(50)) AS Brand
FROM DataSetsMaterializedDataSqlvariant A
WHERE DataSetsMaterializedInternalRowsetID = 1
)Brands On Products.BrandID=Brands.BrandID
INNER JOIN
(
SELECT CAST(A.Col001 AS tinyint) AS ProductCategoryID
,CAST(A.Col002 AS nvarchar(50)) AS ProductCategory
FROM DataSetsMaterializedDataSqlvariant A
WHERE DataSetsMaterializedInternalRowsetID = 2
) ProductCategories On Products.ProductCategoryID=ProductCategories.ProductCategoryID
INNER JOIN
(
SELECT CAST(A.Col001 AS tinyint) AS ProductSubCategoryID
,CAST(A.Col002 AS nvarchar(50)) AS ProductSubCategory
FROM DataSetsMaterializedDataSqlvariant A
WHERE DataSetsMaterializedInternalRowsetID = 11
) ProductSubCategories on Products.ProductSubCategoryID=ProductSubCategories.ProductSubCategoryID
GO
I runs slowly again. Any ideas how to optimize it?

Answer 1

Queries that insert into table variables can't have a parallel plan.
Try using a #temp table instead to allow the SELECT to be parallelised.