Insert Master/Detail Table Using Store Procedure!!!

now i want to learn how to make a stored procedure to insert a record to `purchase` table, and many records to `purchase_detail` table with transaction where the some value are passed from vb6 through the parameters.
i've made a SP to insert 1 record to `purchase` table n 1 record to `purchase_detail` just for testing, so i set the disc value to 10. it works fine...
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CREATE PROCEDURE `usp_save_purchase`(xpurch_id VARCHAR(10),
xpurch_date VARCHAR(10),
xsupp_id VARCHAR(10),
xitem_id VARCHAR(10),
xqty TINYINT(3),
xprice DOUBLE(15,2))

BEGIN
START TRANSACTION;

INSERT INTO purchase(purch_id,purch_date,supplier_id)
VALUES(xpurch_id, xpurch_date, xsupplier_id);

INSERT INTO purchase_detail(purch_id,item_id,qty,price,disc)
VALUES(xpurch_id, xitem_id, xqty, xprice, 10);

COMMIT;

END
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what i need is something like that but i only pass 3 variables (purch_id, purch_date, and supp_id) to SP, and then the SP will insert 1 record of purchase to `purchase` table, and add the purchase items to `purchase_detail` automatically from `purch_temp` table, and use the disc rate based on `supplier_id` and `item_id` from supplier_disc table, which will be looked something like this:
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CREATE PROCEDURE `usp_save_purchase`(xpurch_id VARCHAR(10),
xpurch_date VARCHAR(10),
xsupp_id VARCHAR(10))

BEGIN
START TRANSACTION;

INSERT INTO purchase(purch_id,purch_date,supplier_id)
VALUES(xpurch_id, xpurch_date, xsupplier_id);

/*start looping here
get the disc rate for each items where supp_id = xsupplier_id and item_id = the item_id from purch_temp table, and save it in a local variable (let's say local_disc)

INSERT INTO purchase_detail(purch_id,item_id,qty,price,disc)
VALUES(xpurch_id, xitem_id, xqty, xprice, local_disc);

*/

COMMIT;

END
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can anyone help me please?
thank you in advance...