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Some Basic Concepts In relational terminology, projection is defined as taking a vertical subset from the columns of a single table that retains the unique rows. This kind of SELECT statement returns some of the columns and all of the rows in a table. Projection is implemented through the select list in the SELECT clause of a SELECT statement, as Query 2-2 shows. Query 2-2 SELECT UNIQUE city, state, zipcode FROM customer Query Result 2-2 contains the same number of rows as the customer table, but it projects only a subset of the columns in the table. Query Result 2-2 city state zipcode Bartlesville Blue Island Brighton Cherry Hill Denver Jacksonville Los Altos Menlo Park Mountain View Mountain View Oakland Palo Alto Palo Alto Phoenix Phoenix Princeton Redwood City Redwood City Redwood City San Francisco Sunnyvale Sunnyvale Wilmington OK NY MA NJ CO FL CA CA CA CA CA CA CA AZ AZ NJ CA CA CA CA CA CA DE 74006 60406 02135 08002 80219 32256 94022 94025 94040 94063 94609 94303 94304 85008 85016 08540 94026 94062 94063 94117 94085 94086 19898 Composing Simple SELECT Statements 2-7
