tailieunhanh - SQL VISUAL QUICKSTART GUIDE- P28

SQL VISUAL QUICKSTART GUIDE- P28:SQL (pronounced es-kyoo-el) is the standard programming language for creating, updating, and retrieving information that is stored in databases. With SQL, you can turn your ordinary questions (“Where do our customers live?”) into statements that your database system can understand (SELECT DISTINCT city, state FROM customers;) | Chapter 7 Creating a Self-Join For every biography Listing lists the other biographies that outsold it. Note that the WHERE search condition requires type biography for both tables t1 and t2 because the join condition considers the column type to be two separate columns. See Figure for the result. Tip Using WHERE syntax Listing is equivalent to SELECT AS Better seller AS Higher sales FROM titles tl titles t2 WHERE AND biography AND biography ORDER BY ASC ASC Listing For every biography list the title ID and sales of the other biographies that outsold it. See Figure for the result. Listing SELECT AS Better seller AS Higher sales FROM titles tl INNER JOIN titles t2 ON WHERE biography AND biography ORDER BY ASC ASC title_id sales Better seller Higher sales T06 11320 T12 100001 T06 11320 T07 1500200 T12 100001 T07 1500200 Figure Result of Listing . 250 Joins Listing List all pairs of authors who live in New York state. See Figure for the result. Listing SELECT FROM authors al INNER JOIN authors a2 ON WHERE NY ORDER BY ASC ASC au_fname au_lname au_fname au_lname Sarah Buchman Sarah Buchman Sarah Buchman Christian Kells Christian Kells Sarah Buchman Christian Kells Christian Kells Figure Result of Listing . Listing is a self-join to find all pairs of authors within New York state. See Figure for the result. Tip Using WHERE syntax Listing is equivalent to SELECT FROM authors a1 authors a2 WHERE AND NY ORDER BY ASC ASC Creating a Self-Join 251 Chapter 7 Creating a Self-Join The first and fourth rows of Figure are unnecessary .

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