queryAssignment :: ExperimentId -> UserId -> RunHRRBackend (Maybe Variation)
queryAssignment eid uid conn = do
  ps <- Query.prepare conn selectAssignment
  es <- execute (bind ps (eid, uid))
  ma <- Query.fetchUnique' es
  return $ asVariation <$> ma
queryAssignment :: ExperimentId -> UserId -> RunHRRBackend (Maybe Variation)
queryAssignment eid uid conn = do
  ps <- Query.prepare conn selectAssignment
  es <- execute (bind ps (eid, uid))
  ma <- Query.fetchUnique' es
  return $ asVariation <$> ma
queryAssignment eid uid conn = do
  ps <- Query.prepare conn selectAssignment
  es <- execute (bind ps (eid, uid))
  ma <- Query.fetchUnique' es
  return $ asVariation <$> ma