I love Haskell, but... Haskell is about as popular as SQL? That makes no sense.
In the bigger picture functional programming has made huge inroads. Facebook has a Haskell team whose product handles up to 1 million requests per second, and it's also in production at AT&T, Microsoft, Google, Barclays, New York Times and many smaller outfits. The other day I read about a Haskell-like language being used for high-speed, low-latency trading for a hedge fund.
But there are probably at least 100x more SQL developers out there.
Conversely, there are plenty of weekend Haskellers who enjoy discussing it whenever possible.
How can you tell someone is a Haskeller?
Don't worry; they'll tell you.