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A Long Goodbye - MySQL

Left join. Right join. Inner join. If you've ever wondered what all this jargon means, it's time to find out. Welcome to the wild, the wacky, the insanely cool world of SQL joins.

TABLE OF CONTENTS:
  1. Understanding SQL Joins
  2. Meeting The Family
  3. Keeping It Simple
  4. Crossed Wires
  5. Finding Common Ground
  6. One Step Left...
  7. ...Two Steps Right
  8. The Bookworm Turns
  9. Up A Tree
  10. A Long Goodbye
By: The Disenchanted Developer, (c) Melonfire
Rating: starstarstarstarstar / 247
August 20, 2002

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And that's about it for the moment. In this article, I helped you dip your toes into the deeper waters of SQL, showing you how you could use SQL to massage your resultsets so that you only see the data you want to see. I showed you a basic inner join, the cross join, which will have your database crying for Mommy if you use it too often, and the equi-join, which you can use to filter our unwanted results from your inner join.

Next, I moved on to outer joins, demonstrating how the left and right outer joins can be used to compare tables and isolate the missing or common elements. Finally, I wrapped things up with the self join, a very neat little concept that is sure to come in useful when you're dealing with a single table containing linked records.

In order to avoid having the theory overwhelm you, I also showed you how the various types of joins may be used in real-world situations, to answer basic questions that arise when dealing with linked tables in an RDBMS. Hopefully, the two real-world examples in this article fully demonstrated the value of SQL joins, and also destroyed some of the myths associated with their ease of use (or lack thereof).

This isn't all, though - SQL is very popular on the Web, and there are reams of information out there which will teach you how to manipulate inner and outer joins to do ever more complicated acrobatics. Here are a few good links to get you started:

Speaking SQL, at http://www.devshed.com/c/a/MySQL/Speaking-SQL-part-1/

The MySQL manual, at http://www.mysql.com/doc

The W3School's tutorial on joins, at http://www.w3schools.com/sql/sql_join.asp

CNET's tutorial on joins, at http://asia.cnet.com/itmanager/netadmin/0,39006400,39042301,00.htm

Until next time...au revoir!

Note: All examples in this article have been tested on Linux/i586 with MySQL 4. Examples are illustrative only, and are not meant for a production environment. Melonfire provides no warranties or support for the source code described in this article. YMMV!

 
 
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