Chapter 2

SELECT Statements and Modifying Clauses


Bullet Retrieving data from a database

Bullet Zeroing in on what you want

Bullet Optimizing retrieval performance

The main purpose of storing data on a computer is to be able to retrieve specific elements of the data when you need them. As databases grow in size, the proportion that you are likely to want on any given occasion becomes smaller. As a result, SQL provides tools that enable you to make retrievals in a variety of ways. With these tools — SELECT statements and modifying clauses — you can zero in on the precise pieces of information that you want, even though they may be buried among megabytes of data that you’re not interested in at the moment.

Finding Needles in Haystacks with the SELECT Statement

SQL’s primary tool for retrieving information from a database is the SELECT statement. In its simplest form, with one modifying clause (a FROM clause), it retrieves everything from a table. By adding more modifying clauses, you can whittle down what it retrieves until you are getting exactly what you want, no more and no less.

Suppose you want to display a complete list of all the customers in your CUSTOMER table, including every ...

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