Beginner's SQL: Loop The Output Support

In this second article in the new Beginner's SQL series, a common performance problem is solved. When a database-driven Web page runs a query to retrieve some data, and then uses a value from each row in the result to run an additional query, this "query in a loop" requires excessive and unnecessary database overhead. More importantly, the total time to complete the database retrievals, and thus the resulting Web page download time, balloons. In this article, four examples are shown which "loop the output" and not the query: simple lists, header/detail listings, row differences, and subtotals.