How to INSERT rows based on other rows? - sql-server

Question

I need to run a query that will INSERT new rows into a SQL Server join table.
Suppose I have the following tables to describe which products a store sells and in which states:
products:
+------------+--------------+
| product_id | product_name |
+------------+--------------+
| 1 | Laptop |
| 2 | Aspirin |
| 3 | Mattress |
+------------+--------------+
stores:
+----------+------------+
| store_id | store_name |
+----------+------------+
| 1 | Walmart |
| 2 | Best Buy |
| 3 | Sam's Club |
+----------+------------+
products_stores_states:
+------------+----------+-------+
| product_id | store_id | state |
+------------+----------+-------+
| 1 | 2 | AL |
| 1 | 2 | AR |
| 2 | 2 | AL |
| 2 | 2 | AR |
| 3 | 2 | AL |
| 3 | 2 | AR |
+------------+----------+-------+
So here we see that Best Buy sells all 3 products in AL and AR.
What I need to do is somehow insert rows into the products_stores_states table to add AZ for all products it currently sells.
With a small dataset, I could do this manually, row by row:
INSERT INTO products_stores_states (product_id, store_id, state) VALUES
(1,2,'AZ'),
(2,2,'AZ'),
(3,2,'AZ');
Since this is a large dataset, this is not really an option.
How would I go about inserting a new state for Best Buy for every product_id that the products_stores_states table already contains for Best Buy?
Bonus: If a query could be made to do this for multiple states that the same time, that would be even better.
Right now, I cannot wrap my head around how to do this, but I assume there would need to be a subquery to get the list of matching product_id values I need to use.

Answer 1

The following query will do what you want to do
DECLARE #temp TABLE (
state VARCHAR(20)
)
-- we are inserting state names into a temp table to use it further
INSERT INTO #temp (state)
VALUES
('AZ'),
('MA'),
('TX');
INSERT INTO products_stores_states(product_id, store_id, state )
SELECT
T.product_id,
T.store_id,
temp.state
FROM(
SELECT DISTINCT
Product_id, store_id
FROM
products_stores_states
WHERE store_id = 2 -- the store_id for which you want to make changes
) AS T
CROSS JOIN
#temp AS temp
At first, we are storing the state names into a table variable. Then we need to select only the distinct store_id and product_id combinations for a specific store.
Then we should insert the distinct values cross join with the table variable where we stored state names.
Here is the live demo.
Hope, this helps! Thanks.

Answer 2

If you are positive the inserted state is "NEW" to the table, something like this would work, changing the state variable to whatever you want to insert the new records.
DECLARE #State CHAR(2), #StoreId INT;
SET #State = 'AZ';
SET #StoreId = 2;
INSERT INTO products_stores_states (product_id, store_id, state)
SELECT DISTINCT product_id, #StoreId, #State
FROM dbo.products_stores_states
WHERE store_id = #StoreId;
You could first see what this statement would add using this:
DECLARE #State CHAR(2)
SET #State = 'AZ';
SET #StoreId = 2;
SELECT DISTINCT product_id, #StoreId, #State
FROM dbo.products_stores_states
WHERE store_id = #StoreId;