SQL is an absolute must if you want to work with data. It is powerful and omnipresent in databases. It is also versatile. SQL is usable in just about every analytics program or suite.
SQL is the most commonly sought after programming language in job posting.
SQL is also quite easy to learn. You can be functional at writing queries in a couple of hours. There are nearly countless free resources where you can learn.
Check out the newest video from the Analytics dude, and if you are interested in learning more or finding free resources, click here