I would suggest codeacademy for pure beginner coders! It is incredibly teaches the basics of coding principles. It also makes you to do small projects about your topic in order to enhance your skills. For intermediate-professional coders it is nice to refresh your knowledge about your programming language or you can easily adapt for another programming language by taking another languages because codeacademy knows how to let you stay in that site and continue to press next chapter!

Codeacademy has amazing convincing interface in order to continue your specific course. It has various courses like web development ( php, html, css) and it even makes you an interactive web page with a single course which seems amazing for me! I have completed the php and javascript ( angular js also) courses and I finished at a single shot and I enjoyed a lot! It provides you instructions so you do not stuck like many hours in order to solve the part(s).

i started learning SQL on Codecademy few months back and the experience has been great. THE whole Ui, with the instructions on one side and the SQL software in the middle where you can practice side by side is very engaging. It enables you to track your understanding on the spot and doesnt allow you to go further until you have gotten the previous command correctly.