Are table variables created in memory or in tempdb? Same for
short temp tables?
A temp table will be created in tempdb and you can easily check for it by querying the sysobjects table in tempdb
example
create table #test (Item char(1), TimeSold varchar(20))
select * from tempdb.sys.sysobjects
where name like '#test%'
you should see something with a name like #test_______000000000905 but then with more underscores
If you need to check if a temp table exists then see also How Do You Check If A Temporary Table Exists In SQL Server
The structure of Table variable is also created in tempdb To see the table variable you could do something like this but there is not guarantee that someone didn't sneak in before you when creating his/her table variable. The table variable name will be something like #7BB1235D
declare #v table(id int)
select top 1 * from tempdb.sys.sysobjects
where name like '#%'
and name not like '%[_]%'
order by crdate desc
select * from #v
For more info see here: http://support.microsoft.com/kb/305977
It's been my understanding that, at a minimum, the structure of a table variable is always created in TempDB. Then, as pointed out by SQLMenace, the data may or may not spill over.
Per this Microsoft Knowledge Base Article:
A table variable is not a memory-only
structure. Because a table variable
might hold more data than can fit in
memory, it has to have a place on disk
to store data. Table variables are
created in the tempdb database similar
to temporary tables. If memory is
available, both table variables and
temporary tables are created and
processed while in memory (data
cache).
In MS SQL 2014 was introduced special type of table variables "Memory-Optimized Table Variables". And they don't use tempdb.
See https://msdn.microsoft.com/en-us/library/dn535766.aspx
Related
My data set is too large (about 12 million records) to query. I need to fetch that much amount of data for intermediate calculations. If I use Temp tables, which causes a huge memory consumption.
Is there any mechanisms in SQL Server 2008 R2 onward, which can create temp tables, not in memory, in disk ?
If you declare table like variable
declare #table ...
It is stored in memory.
To store it in db file create temporary table like normal table with # prefix for only your session or ## prefix for all sessions like this:
CREATE table #TMP (
name nvarchar(20)
....
)
You can create it automaticly doing something like this:
select id, name, something_else into #TMP from your_phisical_table
Is it necessary to use # before creating a temporary table in SQL server?
Example:
SELECT column1, column2, someInt, someVarChar
INTO ItemBack1
FROM table2
WHERE table2.ID = 7
For ItemBack1 is it necessary to use the # symbol?
If not, then what is the use of # in creating temp tables?
Yes. You need to prefix the table name with "#" (hash) to create temporary tables.
If you do NOT need the table later, go ahead & create it.
Temporary Tables are very much like normal tables. However, it gets created in tempdb.
Also, it is only accessible via the current session i.e. For EG: if another user tries to access the temp table created by you, he'll not be able to do so.
"##" (double-hash creates "Global" temp table that can be accessed by other sessions as well.
Refer the below link for the Basics of Temporary Tables:
http://www.codeproject.com/Articles/42553/Quick-Overview-Temporary-Tables-in-SQL-Server-2005
If the content of your table is less than 5000 rows & does NOT contain data types such as nvarchar(MAX), varbinary(MAX), consider using Table Variables.
They are the fastest as they are just like any other variables which are stored in the RAM. They are stored in tempdb as well, not in RAM.
DECLARE #ItemBack1 TABLE
(
column1 int,
column2 int,
someInt int,
someVarChar nvarchar(50)
);
INSERT INTO #ItemBack1
SELECT column1,
column2,
someInt,
someVarChar
FROM table2
WHERE table2.ID = 7;
More Info on Table Variables:
http://odetocode.com/articles/365.aspx
The difference between this two tables ItemBack1 and #ItemBack1 is that the first on is persistent (permanent) where as the other is temporary.
Now if take a look at your question again
Is it necessary to Use # for creating temp table in sql server?
The answer is Yes, because without this preceding # the table will not be a temporary table, it will be independent of all sessions and scopes.
I have made one temp table in my database.
My question is "How can i see my temp table in database ?"
Is it physically allocated ?
When you create a table prefaced with a pound sign, it gets created in your tempdb database. Once the procedure calling it is over, it is automatically dropped.
create table #notforlong (id int,catname varchar(20))
It now exists in tempdb
You could find it in sysobjects where name like '#notforlong%'. However, since it goes away outside your proc anyway, I'm not sure it's helpful to refer to it this way.
Your question is completely unclear.
What do you mean by "seeing the table graphically"?
Here's an answer for one interpretation of it as you also mention physical allocation (Assumes: SQL Server 2008)
CREATE TABLE #foo
(
bar int,
baz nchar(100)
)
insert into #foo values (1, REPLICATE('A',100))
select sys.fn_PhysLocFormatter(%%physloc%%) AS RID, bar, baz
FROM #foo /*Returned 1:121:0 for me*/
Then look at that page in SQL Internals Viewer
If I create a temporary table using # sign:
SELECT * INTO #temp FROM dbo.table
Where is this table located? I can't find this from tempdb.
Those tables are created in your tempDB - but the table name might not be exactly as you defined.
In my case, I get:
#temp______________________________000000000003
Try this:
SELECT * INTO #temp FROM dbo.table
SELECT * FROM tempdb.sys.tables
You should see an entry for that temp table you've just created....
When you declare a temporary table, SQL Sever adds some additional characters on its name in order to provide a unique system name for it and then it stores it in tempDB in the sysobjects table. Even though you can query the temporary table with its logical name, internally is known with the exact name SQL Server has set.
How are you looking for them?
If you do a select you'll get the data.
But the table is only available in the session, just for the user who created it (you can have global temp tables).
They are stored in temp db.
Local temp tables can be created using hash (#) sign prior to table name.
They are visible only in current connection. When connection is dropped its scope ends as well.
It is possible to create and use local temp table with the same name simultaneously in two different connections.
Read More
http://sqlnetcode.blogspot.com/2011/11/there-is-already-object-named-temp-in.html
I suspect this issue rose from the fact that if you don't right click and refresh the 'Temporary Tables' folder, SSMS will not show you the temp table immediately.
OMG! What am I doing wrong?
declare #WTF TABLE (
OrderItemId int
)
SELECT TOP 20 OrderItemId as OrderItemId INTO [#WTF] FROM ac_OrderItems
SELECT * FROM [#WTF]
Problem A: This creates a PHYSICAL table called #WTF. WHY?? I thought this was in memory only?!
Problem B: The last line of code, if I do select * from #WTF... WITHOUT the [ ], it returns NOTHING. What is the significance of the [ ]?
I need serious help. I'm losing my MIND!
Thanks in advance.
What you experience is by design:
SELECT…INTO creates a new table in the default filegroup and inserts the resulting rows from the query into it.
The alternatives are to either:
Not define the WTF table, and rely on the behavior to create it automatically
Use the existing code, but change the SELECT INTO into an INSERT:
INSERT INTO #WTF
(orderitemid)
SELECT TOP 20
oi.orderitemid
FROM ac_ORDERITEMS oi
Mind that when using TOP, you should be defining an ORDER BY clause to ensure data is returned consistently.
Because Select INTO always creates a physical table. What you want to do is an Insert Into.
The Select INTO is creating a physical table named '#WTF', just as it's supposed to do.
The secondary answer is that the reason it seemed to only work with brackets [] is because of the # sign.
select * from #WTF
is selecting off of your empty table variable, where as
select * from [#WTF]
is selecting off of the new physical table the select into created that was populated with data. The brackets are used to allow characters not normally allowed in a table or column name so their use here signifies you are looking for a table with the name #WTF instead of a variable named WTF.
All table variables are "physical" tables.
Your belief that they are "memory only" is a myth. They reside in tempdb and are shown in the metadata views with system generated names such as #4BAC3F29. The structure of a table variable is identical to a #temp table.
You cannot use SELECT ... INTO with table variables but can do with #temp tables. Your code just creates a new user table called #WTF in your user database as indicated in the other answers.