Selecting data from two different servers in SQL Server

What you are looking for are Linked Servers. You can get to them in SSMS from the following location in the tree of the Object Explorer:

Server Objects-->Linked Servers

or you can use sp_addlinkedserver.

You only have to set up one. Once you have that, you can call a table on the other server like so:

select
    *
from
    LocalTable,
    [OtherServerName].[OtherDB].[dbo].[OtherTable]

Note that the owner isn't always dbo, so make sure to replace it with whatever schema you use.

SELECT
        *
FROM
        [SERVER2NAME].[THEDB].[THEOWNER].[THETABLE]

You can also look at using Linked Servers. Linked servers can be other types of data sources too such as DB2 platforms. This is one method for trying to access DB2 from a SQL Server TSQL or Sproc call...

Querying across 2 different databases is a distributed query. Here is a list of some techniques plus the pros and cons:

1. Linked servers: Provide access to a wider variety of data sources than SQL Server replication provides
2. Linked servers: Connect with data sources that replication does not support or which require ad hoc access
3. Linked servers: Perform better than OPENDATASOURCE or OPENROWSET
4. OPENDATASOURCE and OPENROWSET functions: Convenient for retrieving data from data sources on an ad hoc basis. OPENROWSET has BULK facilities as well that may/may not require a format file which might be fiddley
5. OPENQUERY: Doesn't support variables
6. All are T-SQL solutions. Relatively easy to implement and set up
7. All are dependent on connection between source and destionation which might affect performance and scalability

I had the same issue to connect an SQL_server 2008 to an SQL_server 2016 hosted in a remote server. Other answers didn't worked for me straightforward. I write my tweaked solution here as I think it may be useful for someone else.

An extended answer for remote IP db connections:

Step 1: link servers

EXEC sp_addlinkedserver @server='SRV_NAME',
   @srvproduct=N'',
   @provider=N'SQLNCLI',   
   @datasrc=N'aaa.bbb.ccc.ddd';
   
EXEC sp_addlinkedsrvlogin 'SRV_NAME', 'false', NULL, 'your_remote_db_login_user', 'your_remote_db_login_password'

...where SRV_NAME is an invented name. We will use it to refer to the remote server from our queries. aaa.bbb.ccc.ddd is the ip address of the remote server hosting your SQLserver DB.

Step 2: Run your queries For instance:

SELECT * FROM [SRV_NAME].your_remote_db_name.dbo.your_table

...and that's it!

Syntax details: sp_addlinkedserver and sp_addlinkedsrvlogin

Simplified solution for adding linked servers

First server

EXEC sp_addlinkedserver @server='ip,port\instancename'

Second Login

EXEC sp_addlinkedsrvlogin 'ip,port\instancename', 'false', NULL, 'remote_db_loginname', 'remote_db_pass'

Execute queries from linked to local db

INSERT INTO Tbl (Col1, Col2, Col3)
SELECT Col1, Col2, Col3
FROM [ip,port\instancename].[linkedDBName].[linkedTblSchema].[linkedTblName]

Created a Linked Server definition in one server to the other (you need SA to do this), then just reference them with 4-part naming (see BOL).

As @Super9 told about OPENDATASOURCE using SQL Server Authentication with data provider SQLOLEDB . I am just posting here a code snippet for one table is in the current sever database where the code is running and another in other server '192.166.41.123'

SELECT top 2 * from dbo.tblHamdoonSoft  tbl1 inner JOIN  
OpenDataSource('SQLOLEDB','Data Source=192.166.41.123;User ID=sa;Password=hamdoonsoft')
.[TestDatabase].[dbo].[tblHamdoonSoft1] tbl2 on tbl1.id = tbl2.id

sp_addlinkedserver('servername')

so its should go like this -

select * from table1
unionall
select * from [server1].[database].[dbo].[table1]

I hope the clarifications all mentioned above, have answered the OP's original question. I just want to add a code snippet for adding SQL Server as a linked server.

At most basic, we can simply add SQL Server as a linked server by executing sp_addlinkedserver with only one parameter @server, i.e.

-- using IP address
exec sp_addlinkedserver @server='192.168.1.11' 
-- PC domain name 
exec sp_addlinkedserver @server='DESKTOP-P5V8JTN'

SQL Server will automatically fill SRV_PROVIDERNAME, SRV_PRODUCT, SRV_DATASOURCE etc. with default values. By doing this, we've to write the IP or PC domain name in the 4 part table address in the query (example below). This can be more annoying or less readable when the linked server will not have a default port or instance, the address will look similar to this 192.168.1.11,1430 or 192.168.1.11,1430\MSSQLSERVER2019.

So, to keep 4 part address short and readable, we can add an alias name for the server instead of the full address by specifying other parameters as follows-

exec sp_addlinkedserver
    @server='ReadSrv1',
    @srvproduct='SQL Server',
    @provider='SQLNCLI',
    @datasrc='192.168.1.11,1430\MSSQLSERVER2019'

But when you'll execute the query, the following error will show- You cannot specify a provider or any properties for product 'SQL Server'. If we keep the server product property value empty '' or any other value, the query will execute successfully.

Next step, make login to the remote linked server by executing the following query-

EXEC sp_addlinkedsrvlogin @rmtsrvname = 'ReadSrv1', @useself = 'false', @locallogin = NULL, @rmtuser = 'sa', @rmtpassword = 'LinkedServerPasswordForSA'

Finally, use the linked server with 4 part address, the syntax is-
[ServerName].[DatabaseName].[Schema].[ObjectName]
Example-

SELECT TOP 100 t.* FROM ReadSrv1.AppDB.dbo.ExceptionLog t

• To list existing linked servers execute:
  exec sp_linkedservers
• To delete a linked server execute:
  exec sp_dropserver @server = 'ReadSrv1', @droplogins='droplogins' (delete login as well) OR
  exec sp_dropserver @server = 'ReadSrv1', @droplogins='NULL' (keep login)