You may think this question is stupid or something but as a new IT student, I think that when i learn one language (ex. java), I tend to forget the one I learned before (ex c)... or I mixed-up the syntax.... So why not merge everything into one so students don't need to learn many languages... then kill the useless programming languages... Why not create a standard like the sql????
Different languages address or embrace:
There are many programming languages which are "general purpose" and others which are specific to a particular situation... but even within the "general purpose" programming languages, no language stands out as being ready to replace all others.
Note that even with your example of SQL, most DB vendors have their own extensions to SQL, which are required to take the database beyond "here's a query, give me a table of results".