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Temporary Tables Vs Table Variables Sql Server 2005


As a rule of thumb, for small to medium volumes of data and simple usage scenarios you should use table variables. (This is an overly broad guideline with of course lots of exceptions - see below and following articles.)

Table variables don't participate in transactions and SELECTs are implicitly with NOLOCK. The transaction behaviour can be very helpful, for instance if you want to ROLLBACK midway through a procedure then table variables populated during that transaction will still be populated!

Using Table Variables within user-defined functions enables those functions to be used more widely (see CREATE FUNCTION documentation for details). If you're writing a function you should use table variables over temp tables unless there's a compelling need otherwise.

Both table variables and temp tables are stored in tempdb. But table variables (since 2005) default to the collation of the current database versus temp tables which take the default collation of tempdb (ref). This means you should be aware of collation issues if using temp tables and your db collation is different to tempdb's, causing problems if you want to compare data in the temp table with data in your database.

It seems generally untrue that there is any difference in quantity of logging (at least for insert/update/delete operations to the table itself though I have since found that there is some small difference in this respect for cached temporary objects in stored procedures due to additional system table updates).

The table variable version actually has a few extra log entries because it gets an entry added to (and later removed from) the sys.syssingleobjrefs base table but overall had a few less bytes logged purely as the internal name for table variables consumes 236 less bytes than for #temp tables (118 fewer nvarchar characters).

A temp table can have indexes, whereas a table variable can only have a primary index. If speed is an issue Table variables can be faster, but obviously if there are a lot of records, or the need to search the temp table of a clustered index, then a Temp Table would be better.

Schema Modifications Schema modifications are possible on temporary tables but not on table variables. Although schema modifi cations are possible on temporary tables, avoid using them because they cause recompilations of statements that use the tables.

The other main difference is that table variables don't have column statistics, where as temp tables do. This means that the query optimiser doesn't know how many rows are in the table variable (it guesses 1), which can lead to highly non-optimal plans been generated if the table variable actually has a large number of rows.

Consider also that you can often replace both with derived tables which may be faster as well. As with all performance tuning, though, only actual tests against your actual data can tell you the best approach for your particular query.

In SQL the Temporary tables are stored in the TempDB and the local temporary tables are only visible in the current session and it will not be visible in another session. This can be shared between nested stored procedure calls. The Global temporary tables are visible to all other sessions and they are destroyed when the last connection referencing table is closed. For Example,

Table variables are similar to tempTables, a table variable is also created in TempDB. The scope of a table variable is the batch, stored procedure, or statement block in which it is declared. They can be passed as parameters between procedures. The same query can be written using Table variable by

Temporary tables are used by every DB developer, but they're not likely to be too adventurous with their use, or exploit all their advantages. They can improve your code's performance and maintainability, but can be the source of grief to both developer and DBA if things go wrong and a process grinds away inexorably slowly. We asked Phil for advice, thinking that it would be a simple e

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