问题
We are experiencing performance problems using a table variable in a Stored Procedure.
Here is what actually happens :
DECLARE @tblTemp TABLE(iId_company INT)
INSERT INTO @tblTemp(iId_company)
SELECT id FROM .....
The SELECT returns 138 results, but inserting in the TABLE variable takes 1min15 but when I use a temp table with the same SELECT, woops, takes 0sec :
CREATE TABLE #temp (iId_company INT)
INSERT INTO #temp(iId_company)
SELECT id FROM ...
What could cause the behavior ?
回答1:
Use a temporary table. You will see much better performance.
A detailed explanation for the reasoning behind this is beyond the scope of the initial question however to summarise:
- A table variable is optimized for one row, by SQL Server i.e. it assumes 1 row will be returned.
- A table variable does not create statistics.
Google temp table Vs. table variable for a wealth of resources and discussions. If you then need specific assistance, fire me an email or contact me on Twitter.
回答2:
Generally, for smaller sets of data, a table variable should be faster than a temp table. For larger sets of data, performance will fall off because table variables don't support parallelism (see this post).
With that said, I haven't experienced, or found experience with such a small set of data being slower for a table variable vs a temp table.
回答3:
Not that it should matter but what does your select look like? I had an issue in SQL Server 2005 where my select on it's own ran relatively fast for what my query was doing say 5 minutes to return all the data over the wire about 150,000 rows. But when I tried to insert that same select into a temp table or table variable the statement ran for more than 1 hour before I killed it. I have yet to figure out what really was going on. I ended up adding the query hint force order and it started inserting faster.
回答4:
Key point about temp tables also is that you can put indexes, etc on them whereas you can't with table variables.
来源：https://stackoverflow.com/questions/1643687/table-variable-poor-performance-on-insert-in-sql-server-stored-procedure