Query Processing
Although I've reviewed the basics of SQL, I haven't yet addressed how the database interprets SQL and how results are gathered. The overall process for resolving a SQL query is known as query processing. It's a topic that has been and continues to be a major focus of database research because of its impact on performance.
As I mentioned earlier, SQL is declarative. Although it provides a language for questions to be asked, it doesn't specify how those questions should be answered. There's no standard. Instead, each vendor has its own strategy. Understanding the details of query processing can provide you with great leverage in tuning database performance. In this section, I provide a simple overview along with an example to give ...
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