A simple DB containing two tables could be:
CREATE TABLE Stock ( StockID INT StockDesc VARCHAR SupplierID INT PRIMARY KEY (StockID) FOREIGN KEY (SupplierID) REFERENCES Supplier(SupplierID))
CREATE TABLE Supplier ( SupplierID INT SupplierName VARCHAR PRIMARY KEY (SupplierID) )
(Assume each stockID has only one supplier)
A typical SQL query would be:
SELECT StockID, StockDesc FROM Stock, Supplier WHERE Stock.SupplierID = Supplier.SupplierID AND SupplierName = "Smiths";
My fundamental understanding of Database design alerts me to the fact that I've already established that there is a relationship between STOCK and SUPPLIER tables via the DDL. Why does SQL need to restipulate that fact again in the first WHERE clause?