Insert up to 10 missing products into a related product discounts table

I have two tables: products and products_discounts. If a product is designated as a "Top 10" product, and it is missing a defined discount in products_discounts, I want to insert a record into products_discounts for each missing record. The inserted values would consist of the product_id and two other hard-coded values in the INSERT INTO.


Products

id, product_id, name, top_ten



Products_Discounts

id, product_id, discount_amount, discount_description

The following is how I plan to do this manually, but since I'll be repeating this process a few times a year, I'm looking to see if this can be done in a few lines of SQL.

(1) Get the list of products that meet my criteria.

SELECT p.product_id, pd.discount_amount FROM products AS p
LEFT OUTER JOIN products_discounts AS pd
    ON p.product_id = pd.product_Id
WHERE p.top_ten = 1
    AND pd.product_id IS NULL

(2) Use a text editor to construct each individual INSERT INTO statement. I'd use the output of step 1 to get the product_ids but the other two values would remain the same (hard-coded).

INSERT INTO products_discounts (product_id, discount_amount, discount_description)
VALUES ('', 10, 'Top 10 Product')

Can these steps be combined into a few lines of SQL?

This might do what you want:

SELECT 'INSERT INTO products_discounts (product_id, discount_amount, discount_description)
VALUES (''' + CONVERT(varchar(30), p.product_id) + ''', 10, ''Top 10 Product'')
'
FROM products AS p
LEFT OUTER JOIN products_discounts AS pd
    ON p.product_id = pd.product_Id
WHERE p.top_ten = 1
    AND pd.product_id IS NULL;

It generates statements for all top-10 products that don't have a product discount. No need to do this in Excel. Just copy-and-paste the results into a new query window in SSMS and run it. Having said that, you'll likely want to automate this procedure, which could be accomplished using either a cursor like this:

DECLARE @cmd nvarchar(max);
DECLARE cur CURSOR LOCAL FORWARD_ONLY STATIC
FOR
SELECT 'INSERT INTO products_discounts (product_id, discount_amount, discount_description)
VALUES (''' + CONVERT(varchar(30), p.product_id) + ''', 10, ''Top 10 Product'')
'
FROM products AS p
LEFT OUTER JOIN products_discounts AS pd
    ON p.product_id = pd.product_Id
WHERE p.top_ten = 1
    AND pd.product_id IS NULL;

OPEN cur;
FETCH NEXT FROM cur INTO @cmd;
WHILE @@FETCH_STATUS = 0
BEGIN
    EXEC sys.sp_executesql @cmd;
    FETCH NEXT FROM cur INTO @cmd;
END
CLOSE cur;
DEALLOCATE cur;

Or in a set-based approach, like this:

DECLARE @cmd nvarchar(max);
SELECT @cmd = CASE WHEN @cmd IS NULL THEN N'' ELSE @cmd END 
    + N'INSERT INTO products_discounts (product_id, discount_amount, discount_description)
VALUES (''' + CONVERT(varchar(30), p.product_id) + ''', 10, ''Top 10 Product'')
'
FROM products AS p
LEFT OUTER JOIN products_discounts AS pd
    ON p.product_id = pd.product_Id
WHERE p.top_ten = 1
    AND pd.product_id IS NULL;

EXEC sys.sp_executesql @cmd;

StackExchange Database Administrators Q#164329, answer score: 6