in Education by
In SQL Server 2005, we can create temp tables one of two ways: declare @tmp table (Col1 int, Col2 int); or create table #tmp (Col1 int, Col2 int); What are the differences between these two? I have read conflicting opinions on whether @tmp still uses tempdb, or if everything happens in memory. In which scenarios does one out-perform the other? JavaScript questions and answers, JavaScript questions pdf, JavaScript question bank, JavaScript questions and answers pdf, mcq on JavaScript pdf, JavaScript questions and solutions, JavaScript mcq Test , Interview JavaScript questions, JavaScript Questions for Interview, JavaScript MCQ (Multiple Choice Questions)

1 Answer

0 votes
by
There are a few differences between Temporary Tables (#tmp) and Table Variables (@tmp), although using tempdb isn't one of them, as spelt out in the MSDN link below. 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.) Some points to consider when choosing between them: Temporary Tables are real tables so you can do things like CREATE INDEXes, etc. If you have large amounts of data for which accessing by index will be faster then temporary tables are a good option. Table variables can have indexes by using PRIMARY KEY or UNIQUE constraints. (If you want a non-unique index just include the primary key column as the last column in the unique constraint. If you don't have a unique column, you can use an identity column.) SQL 2014 has non-unique indexes too. 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! Temp tables might result in stored procedures being recompiled, perhaps often. Table variables will not. You can create a temp table using SELECT INTO, which can be quicker to write (good for ad-hoc querying) and may allow you to deal with changing datatypes over time, since you don't need to define your temp table structure upfront. You can pass table variables back from functions, enabling you to encapsulate and reuse logic much easier (eg make a function to split a string into a table of values on some arbitrary delimiter). 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. Global Temp Tables (##tmp) are another type of temp table available to all sessions and users. Some further reading: Martin Smith's great answer on dba.stackexchange.com MSDN FAQ on difference between the two: https://support.microsoft.com/en-gb/kb/305977 MDSN blog article: https://docs.microsoft.com/archive/blogs/sqlserverstorageengine/tempdb-table-variable-vs-local-temporary-table Article: https://searchsqlserver.techtarget.com/tip/Temporary-tables-in-SQL-Server-vs-table-variables Unexpected behaviors and performance implications of temp tables and temp variables: Paul White on SQLblog.com

Related questions

0 votes
    I'm trying to create a local temp bigquery table in memory for testing purposes. I'm doing this ... JavaScript Questions for Interview, JavaScript MCQ (Multiple Choice Questions)...
asked Jun 3, 2022 in Education by JackTerrance
0 votes
    What is the difference between SUBSTR and CHARINDEX in the SQL Server?...
asked Nov 9, 2020 in Technology by Editorial Staff
0 votes
    How can I determine the space used by a table variable without using DATALENGTH on all columns? eg: DECLARE ... Questions for Interview, JavaScript MCQ (Multiple Choice Questions)...
asked Feb 10, 2022 in Education by JackTerrance
0 votes
    As of SQL Server 2005, you used to be able to open a flat file in SQL Management Studio off the ... JavaScript Questions for Interview, JavaScript MCQ (Multiple Choice Questions)...
asked Mar 7, 2022 in Education by JackTerrance
0 votes
    As of SQL Server 2005, you used to be able to open a flat file in SQL Management Studio off the ... JavaScript Questions for Interview, JavaScript MCQ (Multiple Choice Questions)...
asked Mar 6, 2022 in Education by JackTerrance
0 votes
    I need to remove a highly referenced table in a SQL Server database. How can I get a list of all the ... of the management studio.) Select the correct answer from above options...
asked Jan 28, 2022 in Education by JackTerrance
0 votes
    How can a column with a default value be added to an existing table in SQL Server 2000 / SQL Server 2005? Select the correct answer from above options...
asked Jan 26, 2022 in Education by JackTerrance
0 votes
    Which SQL server table is used to hold the stored procedure scripts?...
asked Nov 9, 2020 in Technology by Editorial Staff
0 votes
    What's the difference between SDK and Runtime in .NET Core?...
asked Feb 16, 2023 in Technology by JackTerrance
0 votes
    I have been working on Power BI for a while now and I often get confused when I browse through help topics of ... two. Please guide me. Select the correct answer from above options...
asked Feb 4, 2022 in Education by JackTerrance
0 votes
    libsvm and liblinear are both software libraries that implement Support Vector Machines. What's the difference? And ... than libsvm? Select the correct answer from above options...
asked Jan 31, 2022 in Education by JackTerrance
0 votes
    What's the difference? What are the advantages/disadvantages of tuples/lists? Select the correct answer from above options...
asked Jan 30, 2022 in Education by JackTerrance
0 votes
    In my textbook I noticed that both these algorithms work almost exactly the same, I am trying to understand ... would be appreciated. Select the correct answer from above options...
asked Jan 26, 2022 in Education by JackTerrance
0 votes
    Are they same? In my view "hadoop fs" command shows the hdfs files and the "hdfs dfs" command shows the local files, why is that? Select the correct answer from above options...
asked Jan 21, 2022 in Education by JackTerrance
0 votes
    What’s the difference between manual testing and automated testing?...
asked Jul 9, 2021 in Technology by JackTerrance
...