See this question: https://stackoverflow.com/questions/31982/looking-for-a-good-book-to-learn-sql
the highest rated answer recommends 2 nice books for beginners.
Coming from C++ field doesn't make much difference in this case in my oppinion. Start from basic stuff and you'll be fine!
For a nice web tutorial you can also check this: http://www.w3schools.com/sql/default.asp
COMMENT: You should not ask for recomendations in SO (although judging by your reputation you are aware of the rules). There are already various answers for this question as it is too generic and subjective. Read some books and tutorials and come back with SQL coding questions ;-)