The syntax to create a temporary table is exactly same as the syntax to create a normal table. But the difference is the table name is prefixed with ‘#’ (pound). By looking at the prefix ‘#’ the sql server understands that it is a temporary table. The following code demonstrates how to create a temporary variable.
1.It is almost similar to normal table with very few exceptions.
2.The scope of the temp table is the current connection session. It can be accessed from any where in same connection session.
3.This table is automatically dropped when the connection session is closed.
4.Different connection sessions creating temporary table with same name will create different copies of the temporary table with the same name. Actually internally the table name is appended with a unique number to support many connection sessions creating tables with same name. You can notice how the table name is uniquely maintained by sql server by running this query. select * from information_schema.tables where table_name like ‘%customer%’
5.foreign key relations cannot be applied to temp tables.
6.Optionally you may drop the table at the end of it’s use. It is a good practice to drop any temporary table after use. drop table #Customer
When you create a temporary table it will be created in tempdb. At the time of table creation the tempdb is locked and hence there is some overhead involved using this. If there are less than 100 records then using temporary tables is not recommended. In such cases you can use table variables which are stored in memory rather than in database(on disk). To learn more about table variables please read this : http://sikarnarender.blogspot.com/2011/11/table-variables-in-sql-server-2005.html