If you are involved in web development, you will eventually find the need to learn SQL.
Also called Structured Query Language, SQL forms the basis for much of the more advanced web development. In order to make more interactive web sites, the information found one the web pages must be stored in databases. To read and write to these databases, you use a language called SQL.
A good resource for learning SQL is found in the W3 Schools tutorial section. After going through the entire lesson, you will feel much more confident in SQL. It is where I always recommend anyone starts there learning of Structured Query Language.