Re: PRIMARY KEY vs. INDEX

To clarify, an indexed field is *not* inheriently unique. You can have an indexed field which is not unique, and a unique field which is not indexed (hence the options being available). A primary key is both indexed and unique (with the slight adaption of compound keys)... but this is majorly off topic. http://www.mysql.com/doc/ - Dan > Christoph, > > Indexes are built on key fields, so yes. When a field is identified as > a key it is indexed. > > To answer your second question, it is the index which maintains the > uniqueness of a field. > > A book is a really good analogy. If you wanted to look up the > references to "string", you can do it very quickly in the index. Even > if you don't come close to the "s" section, you immediately know > whether to look next to the right or to the left. If you push the > issue, and act extremely dumb (like a computer), you'll find the page > containing "string" within 7 hits; once you're on that page it's a > short read to find the term. That's what makes searching on indexed > fields so fast. > > To find the term in the book requires you to start reading on page 1 > and to read text until you find the term. Which why searches which do > not take advantage of key fields are so slow. > > Indexes are your friend, they don't slow down the addition of records > that much, and make retrieval of records extremely fast. > > Regards - Miles Thompson > > > > At 02:13 PM 5/2/2002 +0200, Christoph Starkmann wrote: >>Hi there! >> >>I guess I got a very easy question for the pros here... >>I've been searching the documentaion of mySQL, but didn't >>find the answer (even though I'm sure it's out there >>somewhere :))... >> >>Is a primary key in mySQL automatically indexed? And is a >>unique field indexed automatically ?(I don't think and >>don't hope so, but one never knows) >> >>Thanx, >> >>Kiko >> >>-- >>It's not a bug, it's a feature. >>christoph starkmann >>mailto:kiko@nfq.de >>http://www.gruppe-69.com/ >>ICQ: 100601600 >>-- >> >>-- >>PHP General Mailing List (http://www.php.net/) >>To unsubscribe, visit: http://www.php.net/unsub.php > > > -- > PHP General Mailing List (http://www.php.net/) > To unsubscribe, visit: http://www.php.net/unsub.php -- Dan Hardiker [dhardiker@staff.firstcreative.net] ADAM Software & Systems Engineer First Creative Ltd