SQL certainly is a programming language. It is a member of the declarative family of languages (eg. like Regular Expressions, or Prolog), rather than an imperative/procedural one.
Yea, so is HTML, but if someones list of useful programming languages went C#, HTML, ruby, SQL. You would have to admit too that you would consider that person very inexperianced. It’t like listing a blender in a list of your favorite power tools. It’s not that it’s not useful for what it does, it just doesn’t belong in that particular comparison.
It was originally SEQUEL (Structured English Query Language) and then changed to SQL (Structured Query Language) due to acronym conflict with Hawker Siddeley's trademark.