I just want to ask as new comer to web development, can I learn SQL from the book 'simply sql by rudy limeback' before I start learning about HTML, CSS, PHP,etc or should I have background on PHP for example to learn from that book?
It really, really depends. If you want to get a real tangible webpage ASAP, I'd start with HTML.
SQL is a way to access information, HTML is a way to show it to the world.
I've never read that book, but Rudy is one of the sharper tools in the SP shed (IMHO). I find (unfortunately) that I need to do things the wrong way before I see the full wisdom of his ways.
I'd probably go HTML, CSS, PHP, SQL. SQL requires a mental discipline that would be invaluable in learning the others, but I think I'd miss some of the more subtle things about structure if I hadn't stumbled around a bit before I dabbled in SQL.
Hope I made at least some sense there...