In Chapter 1, we saw that an entity’s attributes are contained in a set of related tables. Each table contains records (or instances) about the entity. Each record is composed of related sets of attributes about the entity. In order to produce information about the entity, the attribute values must be retrieved from the database tables in which they reside. This is done using an SQL command called a SELECT statement, which is a powerful tool for extracting attributes from a database and producing information.
SELECT statements contain six clauses:
|•SELECT||Identifies the attributes retrieved from the database|
|•FROM||Identifies the table(s) that contains the attributes|
|•WHERE||Contains conditions used to identify ...|