hi everybody , I want to master the SQL injection , so can u guys tell me where to learn
Theres no secret trick. Learn SQL (find a pdf) then learn the basics of sql injection. Master it with internet reserches. Setup a website with sql database then try to access it.
Codecademy is a great place to start learning SQL. Once you know how a language works you can better prepare your methodology for exploiting it.
There are dozens of injection tutorials laying around null-byte, and dozens more on the web.
As mentioned by Se7en, learn how things works, then you can break it, instead of following a tutorial blindly.