What is the best way to learn SQL ?

You can go through the website and practice your own

configure sql in ur system and use w3schools website tutorials .
it's very helpful for u as a beginner

you can download a free version of microsoft sql server and from microsoft website and download some lectures and start practice

The fisrt way is to learn Relational algebra.

Go to www.w3schools.com and learn SQL with examples or click on this below link to download a pdf file from which you can learn SQL in21 days.
http://www.fdi.ucm.es/profesor/albertoe/grupodesarrollo/sql/material/%28ebook%20pdf%29%20teach%20yourself%20sql%20in%2021%20days.pdf

Practice, using a textbook to learn it won't help a lot if you don't practice

I've only tried learning it one way, and that way worked very beautifully.
It's in w3 schools.
Check this link:- http://www.w3schools.com/sql/default.asp Everything in that tutorial is very basic, and they structure the difficulty of each section so you wouldn't have to move to unnecessary advanced stuff.