Question: I am creating a classifieds website.

Im storing all ads in mysql database, in different tables.

Is it possible to find these ads somehow, from googles search engine?

Is it possible to create meta information about each ad so that google finds them?

How does major companies do this?

I have thought about auto-generating a html-page for each ad inserted, but 500thousand auto-generated html pages doesn't really sound that good of a solution!

Any thoughts and idéas?

**UPDATE**:
Here is my basic website so far:
(ALL PHP BASED)
I have a search engine which searches database for records.
After finding and displaying search results, you can click on a result ('ad') and then PHP fetches info from the database and displays it, simple!
In the 'put ad' section of my site, you can put your own ad into a mysql database.

I need to know how I should make google find ads in my website also, as I dont think google-crawler can search my database just because users can.

Please explain your answers more thoroughly so that I understand fully how this works!

Thank you

Answer: 
If you want Google to index your site, you need to put all your pages on the web and link between them.

You do not have to auto-generate a static HTML page for everything, all pages can be dynamically created (JSP, ASP, PHP, what have you), but they need to be accessible for a web crawler.
Google can find you no matter *where* you try to hide. Even if you can somehow fit yourself into a mysql table. Because they're Google. :-D

Seriously, though, they use a bot to periodically spider your site so you mostly just need to make the data in your database available as web pages on your site, and make your site bot-friendly (use an appropriate robots.txt file, provide a search engine-friendly site map, etc.) You need to make sure they can *find* your site, so make sure it's linked to by other sites -- preferably sites with lots of traffic.

If your site only displays specific results in response to search terms you'll have a harder time. You may want to make full lists of the records available for people without search terms (paged appropriately if you have lots of data).