queryHello.hs

import Data.Int (Int32)
import Database.Record.Instances ()
import Database.Relational.Query

hello :: Relation () (Int32, String)
hello =  relation $ return (value 0 >< value "Hello")

world :: Relation () (Int32, String)
world =  relation $ return (value 0 >< value "World!")

helloWorld :: Relation () ((Int32, String), (Int32, String))
helloWorld = relation $ do
  h <- query hello
  w <- query world
  on $ h ! fst' .=. w ! fst'
  return $ h >< w

main :: IO ()
main =  print helloWorld