SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 1)
   ExpressionList (children 1)
    Function concat (children 1)
     ExpressionList (children 2)
      Function map (children 1)
       ExpressionList (children 2)
        Literal \'key5\'
        Literal UInt64_500
      Function map (children 1)
       ExpressionList (children 2)
        Literal \'key6\'
        Literal UInt64_600