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: 
How would you normally access these classifieds? You're not just keeping them locked up in the database, are you?

Google sees your website like any other visitor would see your website. If you have a normal database-driven site, there's some unique URL for each classified where it it displayed. If there's a link to it somewhere, Google will find it.
First Create a PHP file that pulls the index plus human readable reference for all records. 

That is your main page broken out into categories (like in the case of Craigslist.com - by Country and State). 

Then each category link feeds back to the php script the selected value regardless of level(s) finally reaching the ad itself. 

So, If a category is selected which contains more categories (like states contain cities) Then display the next list of categories. Else display the list of ads for that city. 

This will give Google.com a way to index a site (aka mysql db) dynamically with out creating static content for the millions (billions or trillions) of records involved.

This is Just an idea of how to get Google.com to index a database.