SQL SERVER – Difference TempTable and Table Variable – TempTable in Memory a Myth

转自 http://blog.sqlauthority.com/2009/12/15/sql-server-difference-temptable-and-table-variable-temptable-in-memory-a-myth/

Recently, I have been conducting many training sessions at a leading technology company in India. During the discussion of temp table and table variable, I quite commonly hear that Table Variables are stored in memory and Temp Tables are stored in TempDB. I would like to bust this misconception by suggesting following:

Temp Table and Table Variable — both are created in TempDB and not in memory.

Let us prove this concept by running the following T-SQL script.

/* Check the difference between Temp Table and Memory Tables */
-- Get Current Session ID
SELECT @@SPID AS Current_SessionID
-- Check the space usage in page files
SELECT user_objects_alloc_page_count
FROM sys.dm_db_session_space_usage
WHERE session_id = (SELECT @@SPID )
GO
-- Create Temp Table and insert three thousand rows
CREATE TABLE #TempTable (Col1 INT)
INSERT INTO #TempTable (Col1)
SELECT TOP 3000 ROW_NUMBER() OVER(ORDER BY a.name)
FROM sys.all_objects a
CROSS JOIN sys.all_objects b
GO
-- Check the space usage in page files
SELECT user_objects_alloc_page_count
FROM sys.dm_db_session_space_usage
WHERE session_id = (SELECT @@SPID )
GO
-- Create Table Variable and insert three thousand rows
DECLARE @temp TABLE(Col1 INT)
INSERT INTO @temp (Col1)
SELECT TOP 3000 ROW_NUMBER() OVER(ORDER BY a.name)
FROM sys.all_objects a
CROSS JOIN sys.all_objects b
GO
-- Check the space usage in page files
SELECT user_objects_alloc_page_count
FROM sys.dm_db_session_space_usage
WHERE session_id = (SELECT @@SPID )
GO
-- Clean up
DROP TABLE #TempTable
GO

Let us see the resultset. It is very clear that the size of the table variable and temp table is the same and created in TempDb.

SQL SERVER – Difference TempTable and Table Variable – TempTable in Memory a Myth

Have you ever heard of this misconception? Do you know any other method to prove that both Temp Table and TableVariable are created in TempDB.

Update : Ken Simmons have written excellent another article proving without inserting data that temp table and table variable both are created in TempDB please read here.

Reference: Pinal Dave (http://blog.SQLAuthority.com)