Do anyone know a great database or software to build websites like a myspace, facebook, or a youtube website?
All I know about is MySQL. I am very pleased with it. I use PHPMyAdmin to work with it, and everything's nice and straightforward.
How big do you expect the site to get to? What type of hardware are you hosting on, Platform, CPU's, RAM, etc...? MySQL may not be a good match for your intended size and usage.
Depends on the amount of data and processing you are doing. Oracle and MSSQL for big jobs, normal website traffic MySQL and Postgres
MySQL works fine and very affordable. If your site goes as big as these guys you mentioned, you will probably hire staff to take care of the R&D.
mysql + phpmyadmin is probably one the most support db's out there. I know our guys prefer it over anything else.
MySql is the best database you can find out there to perform your jobs. And they are open source. Really interesting tool.
Can you please define "the best database" ? If you build a blog and expect 10 users daily, keep going with MySQL of course. For a while I make some stress tests to my either remote and local servers. And since I replaced db from MySQL to Firebird, I lowered CPU usage from 95% to ranges between 10% and 50%. I encourage you to try FireBird's new version 2.5 Alpha if you have or expect =>50K users.
That depends on ur application design. If u r going with linux u have to use my sql. If u are designing an application on .net u can use either Ms-Access or Ms-Sql. Its better to go with my sql as it is a open source.