SQL Injection Tutorial: All common SQL injection problems and Solutions

Hello,
    Today an tutorial for you what covers most problems while doing SQL injection and solutions to them. Probably every person who has looked at tutorials to hack a website have noticed that there are too much SQL tutorials. Almost every forum has 10 tutorials and blogs 5 tutorials about SQL injection, but actually those tutorials are stolen from somewhere else and the author doesn't probably even know why does SQL injection work. All of those tutorials are like textbooks with their ABC's and the result is just a mess. Everyone are writing tutorials about SQL, but nobody covers the problems what will come with that attack.

What is the cause of most problems related to SQL injection?

Webdevelopers aren't always really dumb and they have also heard of hackers and have implemented some security measures like WAF or manual protetion. WAF is an Web application firewall and will block all malicous requests, but WAF's are quite easy to bypass. Nobody would like to have their site hacked and they are also implementing some security, but ofcourse it would be false to say that if we fail then it's the servers fault. There's also a huge possibility that we're injecting otherwise than we should.