SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 2)
   ExpressionList (children 1)
    Function map (alias m) (children 1)
     ExpressionList (children 2)
      Literal \'a\'
      Function map (children 1)
       ExpressionList (children 2)
        Literal UInt64_1
        Literal \'foo\'
   ExpressionList (children 2)
    Function arrayElementOrNull (children 1)
     ExpressionList (children 2)
      Identifier m
      Literal \'a\'
    Function arrayElementOrNull (children 1)
     ExpressionList (children 2)
      Identifier m
      Literal \'c\'
