You have two tables named
tableProducts with Columns ProductID, ProductName, and ProductPrice AND tableQuantity with columns QuantityID and AvailableQuantity. Please help me.
Question No . 1 You are selecting both columns from tableProducts then why you are running join query or your query incomplete .
Ok
following is the structure of query Please try
SELECT P.ProductName
,P.ProductPrice
FROM tableProducts P
INNER JOIN tableQuantity Q ON (P.ProductID = Q.QuantityID)
WHERE P.ProductID= txtid.Text