If Web 2.0 is about user generated content and sociality, then the online manuals for PHP and MySQL are Manuals 2.0. The user comments at the bottom of each page are among the most useful parts of each manual. (The PHP manual has the added benefit of being able to look up any function by http://www.php.net/function-name.)

For example, here are two great MySQL tips I learned from the user comments (this isn’t in the stock manual):

Posted by Adam Tylmad on August 25 2004 12:36pm
If you want to ORDER BY [columnname] ASC
and have the NULL rows in the bottom
you can use ORDER BY -[columnname] DESC

Here’s how you can put the U.S. and U.K. at the top of your “country” list:

Posted by Gregory Turner on March 10 2005 5:00pm
SELECT * FROM countries
 ORDER by iso_code IN ('UK', 'US') desc;

Which returns something like:
 UK   United Kingdom
 US   United States
 AF   Afghanistan
 AL   Albania
 ...

I wish all manuals were this good.