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Local Temporary Tables and Table Variables


Local Temporary Tables and Table Variables

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GilaMonster
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Yes, I did.

Gail Shaw
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Thanks. That is what I thought.



Jason AKA CirqueDeSQLeil
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smeet.sinha
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One more major diff.


You can not use temp tables in UDF
But can use table variables in UDF....
Jeff Moden
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True enough. You should also mention that most UDFs aren't necessary either. :-)

--Jeff Moden

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GilaMonster (8/31/2008)
Very nice.

Just one small thing. You say that for data storage, temp tables are in TempDB and table variables are in memory and tempDB. I may be misunderstanding what you mean there, but temp tables are also memory resident unless it becomes necessary to write them to disk (memory pressure, too large a table)


Also, the Appendix states that table variables are held in memory and temporary tables are held in tempdb. Whilst usually correct*, it is also the case that both are physically created in tempdb, as can be demonstrated by running the following code on a SQL Server which has no other activity occurring (runs on SQL 2000, 2005 and 2008):

-- make a list of all of the user tables currently active in the
-- TempDB database
if object_id('tempdb..#tempTables') isnot null droptable #tempTables
select name into #tempTables from tempdb..sysobjectswhere type ='U'
-- prove that even this new temporary table is in the list.
-- Note the suffix at the end of it to uniquely identify the table across sessions.
select * from #tempTables where name like '#tempTables%'
GO
-- create a table variable
declare@MyTableVariable table (RowID int)
-- show all of the new user tables in the TempDB database.
select name from tempdb..sysobjects
where type ='U' and name notin (select name from #tempTables)
GO



* According to KB305977, a table variable can hold more data than could fit into memory.
http://support.microsoft.com/default.aspx?scid=kb;en-us;305977&Product=sql2k
Go


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