Codecademy

Level:

Price: Free!

Python, HTML/CSS, Java, JavaScript, SQL, Ruby

MySQL Tutorial

Level:

Price: Free!

SQL

CodeHS

Level:

Price: $25/month

Python, HTML/CSS, Java, JavaScript, SQL, C, C++

Khan Academy

Level:

Price: Free!

HTML/CSS, JavaScript, SQL

Learn SQL The Hard Way

Level:

Price: Free!

SQL

Vertabelo Academy

Level:

Price: Free!

SQL