SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 1)
   ExpressionList (children 2)
    Function arrayElementOrNull (children 1)
     ExpressionList (children 2)
      Identifier m
      Literal UInt64_0
    Function materialize (alias m) (children 1)
     ExpressionList (children 1)
      Function map (children 1)
       ExpressionList (children 2)
        Literal \'key\'
        Literal UInt64_42
