SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 3)
   ExpressionList (children 1)
    Literal UInt64_1 (alias global_a)
   ExpressionList (children 1)
    Identifier b.a
   TablesInSelectQuery (children 1)
    TablesInSelectQueryElement (children 1)
     TableExpression (children 1)
      Subquery (alias b) (children 1)
       SelectWithUnionQuery (children 1)
        ExpressionList (children 1)
         SelectQuery (children 1)
          ExpressionList (children 1)
           Identifier global_a (alias a)