@tableName Table variables are alive for duration of the script running only i.e. they are only session level objects.
To test this, open two query editor windows under sql server management studio, and create table variables with same name but different structures. You will get an idea. The @tableName object is thus temporary and used for our internal processing of data, and it doesn't contribute to the actual database structure.
There is another type of table object which can be created for temporary use. They are #tableName objects declared like similar create statement for physical tables:
Create table #test (Id int, Name varchar(50))
This table object is created and stored in temp database. Unlike the first one, this object is more useful, can store large data and takes part in transactions etc. These tables are alive till the connection is open. You have to drop the created object by following script before re-creating it.
IF OBJECT_ID('tempdb..#test') IS NOT NULL
DROP TABLE #test
Hope this makes sense !