SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 2)
   ExpressionList (children 1)
    Subquery (children 1)
     SelectWithUnionQuery (children 1)
      ExpressionList (children 1)
       SelectQuery (children 2)
        ExpressionList (children 1)
         Identifier a
        TablesInSelectQuery (children 1)
         TablesInSelectQueryElement (children 1)
          TableExpression (children 1)
           Subquery (children 1)
            SelectWithUnionQuery (children 1)
             ExpressionList (children 1)
              SelectQuery (children 1)
               ExpressionList (children 1)
                Literal UInt64_1 (alias a)
   Set
