How Queries are Processed by RDM SQL

A query optimizer is the component of an SQL system that attempts to determine the best way to retrieve the data that is needed to produce the results specified by a given SELECT statement. The problem with the term "query optimizer" is that it makes it sound like it can take a stupidly formulated query and turn it into one that executes at optimal performance. The fact is, query optimizers are just not that smart. So, it is important that queries be reasonably formulated and the more you understand how the optimizer goes about its business the better equipped you will be to do just that. That is what this chapter is all about. Here you will …

• learn how the RDM SQL optimizer works,
• learn the different ways in which data can be retrieved from a database,
• be given guidelines on how to construct fast-performing queries, and
• learn how to retrieve and interpret a query's access plan.