December 2002
Beginner
640 pages
16h 41m
English
Imagine that you have a busy database. Perhaps it's an online store, and clients are performing read and write accesses almost constantly. While some clients are trying to read data from a table (for example, to see what products are available), others are trying to insert data or perform an update (to place an order).
Assume that you have a table containing the stock levels in the online store. There's a table called stock_level, and in it there are columns called product_id, to identify the product by ID, and qty, which holds the current quantity in stock for each item.
If a customer tries to order an item, the server application checks the quantity in stock by running a SELECT query on this table. If the number in stock ...