dbo.dbo is this valid?

Is this valid dbo.dbo, if so what does it mean? I have spoted this on a query that someone else wrote:

from dbo.tm开发者_Python百科p_BDCode aob inner join dbo.dbo.tmp_BDCode_03 ao

Would it have an adverse effect on a query, because dbo just means its a global object.

Thanks all for clarification on this.

There may be a database named dbo or schema named dbo.dbo or a table named dbo.tablename.

These commands are valid:

create database dbo
use dbo
create schema [dbo.dbo]
create table [dbo.dbo].[dbo.tablename] (id int, name varchar(10))

select * from [dbo.dbo].[dbo.tablename] as dt
select * from dbo.[dbo.dbo].[dbo.tablename] as dt

It definitely has an adverse effect of not being clear enough to the programmers that will have to read this source code afterwards.