Global Temporary Table

Question

Hi I am not getting the concept of global temporary table in sql server and how can we create it ?

Satyapriya Nayak · Answer

Hi Shubham Global temporary table:- Global temporary table is created in the tempdb and it is visible to all other sessions as well. Global temporary tables are only destroyed when the current user disconnected and all the sessions referring to it closed. It means no user sessions refers it. Since the global temporary table is created in the tempdb whenever we use temporary tables there is a interaction between the two database (tempdb and the database in which block of code is written) which may slow down the performance. Global temporary table can be used in Joins. Global table is created with the help of the ##. The syntax for creating the global temporary table is given below: create table ##[table name] (col1 datatype col2 datatype ......coln datatype) For example the syntax to create the global temporary table ##employeedetails is given below: CREATE table ##employeedetails (id int identity(11) empFname nvarchar(100) empEname nvarchar(100) empdate datetime) We can also create indexes on the Global temporary tables. For example Create index indx_GTT on ##employeedetails (empFname) We can also define constraints on the Global temporary tables. For Example Alter table ##employeedetails add constraint pk_GTT primary key(id) Similar to physical table and local temporary table the values in the global temporary table can also be inserted with the help of the Insert command. For example to insert the value in the global temporary table ## employeedetails  we can use the following SQL Statement: Insert into ## employeedetails ( empFname  empEname  empdate ) Values ( 'Vivek' ' Johari' getdate()) We can access the global table within the stored procedure in which it is defined and also in the stored procedure which is called inside this stored procedure. Create procedure test_GTT as begin CREATE table ##employeedetails (id int identity(11) empFname nvarchar(100) empEname nvarchar(100) empdate datetime) exec insert_GTT select * from ##employeedetails drop table ##employeedetails end Create procedure insert_GTT as begin Insert into ##employeedetails ( empFname  empEname  empdate ) Values ( 'Vivek' ' Johari' getdate()) end In the above example we create a global temporary table ##employeedetails in the stored procedure test_GTT. This procedure call another procedure insert_GTT. The procedure contains the Insert command for the table ##employeedetails. When we execute the procedure test_GTT it will give the following result. Exec test_GTT Global temporary tables are itself dropped when the current user session is closed and no other user is referring to it but it is better to drop it manually at the end of the block of the code in which it is defined or at the end of the stored procedure in which it is defined. The global temporary tables can viewed with the help of the system view 'sys.objects'. SELECT * FROM sys.objects where type='U' Transactions are also applicable on the Global temporary tables. Alter procedure test_GTT as begin begin transaction CREATE table ##employeedetails (id int identity(11) empFname nvarchar(100) empEname nvarchar(100) empdate datetime) exec insert_GTT rollback select * from ##employeedetails drop table ##employeedetails end If we execute the above procedure the it will give the following output. Limitations:- We can't use global temporary table inside a SQL Function. We can't create triggers on the temporary tables. We can create View on the temporary tables. Please refer the below link http://www.sqlservercentral.com/blogs/vivekssqlnotes/2012/01/07/sql-server-global-temporary-tables/ Thanks

Senthilkumar · Answer

Hi Shubham A global temporary table is visible to any session (connection on server) while in existence. It lasts until all users that are referencing the table disconnect. A local temporary table like #California below is visible only the local session (connection) and child session created by dynamic SQL (sp_executeSQL). The temporary table is localized by an auto-generated suffix which is added to the table name. It is deleted after the user disconnects. In some applications global temporary tables offer better performance than local or table variables. A global temporary table is created using CREATE TABLE statement with the table name prefixed with a double number sign (##table_name). In SQL Server global temporary tables are visible to all sessions (connections). So if you create a global temporary table in one session you can start using it in other sessions. Session 1 CREATE TABLE ##temp1 (c1 INT); INSERT INTO ##temp1 VALUES (1); Session 2 SELECT * FROM ##temp1 For example SELECT * INTO ##tmpemp FROM employees Now the all sql server connection sessions can use this ##tmpemp table. For more info: http://www.sqlines.com/articles/sql-server/local_and_global_temporary_tables