SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 2)
   ExpressionList (children 1)
    Function count (children 1)
     ExpressionList
   TablesInSelectQuery (children 1)
    TablesInSelectQueryElement (children 1)
     TableExpression (children 1)
      Function icebergS3 (children 1)
       ExpressionList (children 3)
        Identifier s3_conn
        Function equals (children 1)
         ExpressionList (children 2)
          Identifier filename
          Literal \'merged_several_tables_test\'
        Set
