If you alter a temporary table, or modify the data in them, you may incur recompiles of the parent routine. However, if you follow a few simple rules, they are a good choice for intermediate ‘working’ tables, and for passing results between routines, where the data sets are small and the processing required is relatively straightforward. Even then, performance can suffer badly, especially if you’re performing more complex processing, because the optimizer still has no access to statistics, and so no knowledge of the selectivity of any query predicate. Phil Factor illustrates the 'quirks' of the SQL_VARIANT datatype and why it's best to investigate when SQL Prompt alerts you to its use. The local variable type is table; table is the type of variable. We discovered this with stored procedures that were written with table variable (the SQL Server docs say they're better than temp tables all the way around). Why not just process this result set once and throw the records into a SQL temp table? First, we declared a Table Variable. … So for most scripts you will most likely see the use of a SQL Server temp table as opposed to a table variable. Also like local SQL temp tables, table variables are accessible only within the session that created them. For the temp table queries the optimizer, armed with a full knowledge of cardinality and the metadata from the primary key constraints, chooses an efficient Merge Join operator to perform the join operation. Many believe that table variables exist only in memory, but that is simply not true. You’ll see the queries shortly, when I show the code for the Test Rig. SQL Prompt implements this recomendation as a code analysis rule, ST011 – Consider using table variable instead of temporary table. Interestingly, the two “common words in Dracula” queries that were fast even on heaps are now much slower. Table variables tend to get ‘bad press’, because queries that use them occasionally result in very inefficient execution plans. If the volume of data is less, say less than 100 rows. Even the indexes that enforce PRIMARY KEY and UNIQUE constraints on table variables do not have statistics. When the batch starts executing, the hint will cause only that single statement to recompile, at which point the table variable will be populated and the optimizer can use the real row count to compile a new plan for that statement. I will blog about it in the separate blog post. In short, it is easier to keep things neat and tidy. While you can now use the inline index creation syntax to create non-clustered indexes on a table variable, there are some restrictions, and there are still no associated statistics. Armed with the correct row counts, the optimizer changes its strategy, but because it still has none of the useful metadata available to it when we define constraints and keys, it makes a bad choice. You can use the same name that you declared as it’s confined to that session. Global SQL temp tables are useful when you want you want the result set visible to all other sessions. However, unlike SQL temp tables the table variable is only accessible within the current batch. You need to make sure to clear up after yourself, to avoid tempdb congestion. People can, and do, argue a great deal about the relative merits of table variables and temporary tables. As with the other scenarios when deleting based on the indexed column the temporary table performs better than the table variable. Like with temp tables, table variables reside in TempDB. In fact, the table variable provides all the properties of the local variable, but the local variables have some limitations, unlike temp or regular tables. Table variables also require fewer locking resources as they are ‘private’ to the process and batch that created them. For example, you want to process data for a SQL statement and it you need a place to store items for your loop to read through. 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Because the optimizer in some cases may ignore the number of records in table variable while generating the query plan. This becomes less efficient the larger the data sets, and is especially bad in the cases where it scans the CommonWords table variable, because it results in over 60K seeks of the Dracula table variable. Table variables are created like any other variable, using the DECLARE statement. Lastly, we are selecting all the records from Table Variable, whose Total Income is … The compromises in the design of table variables, such as the lack of statistics and recompiles, work against them if the data is volatile. So there is a lot of flexibility and allows the developer to be quite creative. Sometimes, but rarely, even this won’t help. table variables and local temporary tables (ref. You can use your existing read access to pull the data into a SQL Server temporary table and make adjustments from there. This is the primary reason, why my Comprehensive Database Performance Health Checkis just a maximum of 4 hours of service, as in most cases, we fix the problem in just a few minutes and spend the rest o… This advantage the #temp table has over the @table variable is not often spoken about, but in my experience it’s a big one. Let’s try it out. At a certain point, you will also need to trigger a recompile to get a decent execution plan, which has its own overhead. We leave out the poor heaps for the time being. Bad. When you are trying to load the data, the behavior of the Temp Table and Table variable is pretty much the same. You can create a temp table with either a create table statement or the into clause in a select statement. What’s the performance like if we join two table variables? Let’s say you want full DDL or DML access to a table, but don’t have it. In fact it is the means of returning result set in table-valued user defined functions. You can create a Table Variable within a UDF, and modify the data using one of the DML statements, this is not possible with Temp-Tables. Armed with correct row counts and ordered inputs, the optimizer chooses the far more efficient Merge Join. Viewed 478 times 0. CTE stands for Common Table Expressions. View all posts by Aamir Syed, © 2020 Quest Software Inc. ALL RIGHTS RESERVED. He started his IT career in helpdesk world and eventually moved into the networking/systems administrator side of things. Despite having once been shouted at by a furious Bill Gates at an exhibition in the early 1980s, he has remained resolutely anonymous throughout his career. Aamir is a SQL Server Database Administrator in the NYC/NJ area (and has recently taken a role as a Database Developer). Following are the results of the initial test runs. They reside in the tempdb database much like local SQL Server temp tables. It scans the CommonWords heap then attempts a “partial aggregation”, estimating that it will aggregate down from 60K rows to a few hundred. It is very beneficial to store data in SQL Server temp tables rather than manipulate or work with permanent tables. They are easier to work with and they trigger fewer recompiles in the routines in which they’re used, compared to using temporary tables. In SQL, temp tables and table variables are used to save or store data in temporary basis.Both are almost same, but have some difference. Phil Factor (real name withheld to protect the guilty), aka Database Mole, has 30 years of experience with database-intensive applications. E.g. I won’t delve into the details of the execution plans behind these performance metrics, other than to give a few broad explanations of the main differences. Even with relatively modest row counts, you can encounter query performance issues if you try to execute a query that is a join, and you forget to define a PRIMARY KEY or UNIQUE constraint on the column you are using for the join. Which is something that I would recommend. SQL temp tables are created in the tempdb database. Often it is very easy to fix them and we can improve the performance of the server in just few minutes. Once it moved to production, the system screeched to a halt. They are not visible outside of the batch, meaning the concept of session hierarchy can be somewhat ignored. Temporary Table vs Table Variable The TestTVsAndTTs download includes the script to create these two tables and populate each one from its associated text file. Pros and cons of table variables and temporary tables Table variables tend to get ‘bad press’, because queries that use them occasionally result in very inefficient execution plans. One of the most often used scenarios for SQL Server temp tables is within a loop of some sort. But Session 1, which is above session 2, will not be able to see the SQL Server temp table. My point is that table variables are NOT always better nor are temp tables always better. Otherwise a SQL Server temp table is useful when sifting through large amounts of data. Temp table operations are carried out as part of the user transaction itself, whereas table variable operations are carried out as system transactions, independent of any outer user transaction. Not only does this save on expensive query processing, but it may even make your code look a little cleaner. We’ll start with an example where a table variable is ideal, and results in better performance. The puzzling part is the same stored procedure now running a lot slower. I tend to like temp tables in scenarios where the object is used over a longer period of time – I can create non-key indexes on it and it's more flexible to create to begin with (SELECT INTO can be used to create the temp table). However, unlike SQL temp tables the table variable is only accessible within the current batch. The estimated plans looked the same using temp table and table variable… So table variable is faster then temporary table. All you need to know about temporary tables When to use #t or ##t or when to declare a table variable @t we will go in depth and compare the differences and performances and some myths about temp tables Temporary Tables are two types Local temporary tables : Global temporary tables : … Finally, we run the same queries with temporary tables. Please note that this is the test rig in its final form showing roughly equal performance for the three different types of table. Ask Question Asked 2 years, 9 months ago. In this article, you will learn about the main differences between Temp Table, Table variable and CTE. The results show that when the table variables are heaps, you run the risk of the query running for ten minutes rather than 100 milliseconds. No need to setup permissions. For example: #Table_name. Let me paint a picture of the first scenario. It provides a quick and efficient means to do so. They are also not fully logged, so creating and filling them is faster and requires less space in the transaction log. Interestingly, the two “common words in Dracula” queries perform much better and this is because, for those two, the optimizer chose instead a Hash Match join. As you can see, the performance advantage of the temporary table vanishes. All in a day's work for a developer armed with SQL Prompt. Also note that anyone can DROP the table. All tests were run, deliberately, on a slow development server, for purposes of illustration; you will get very different results with a production server. The more rows in the table variable, the larger the discrepancies between estimation and reality, and the more inefficient become the optimizer’s plan choices. If a table variable is declared in a stored procedure, it is local to that stored procedure and cannot be referenced in a nested procedure There are also no statistics-based recompiles for table variables and you can’t ALTER one, so routines that use them tend to incur fewer recompiles than those that use temporary tables. It is only safe to store data as a SQL_VARIANT, if you explicitly convert it to its true type before you use it. They are scoped to the batch or routine in which they are created, and are removed automatically once it completes execution, and so using them within a long-lived connection doesn’t risk ‘resource hogging’ problems in tempdb. We’re dealing with a small data set (291 rows). Here is a quick example of setting up and using a table variable. Microsoft recommends to use Temp Table if you have more than 100 rows of data. Phil Factor demonstrates the use of temporary tables and table variables, and offers a few simple rules to decide if a table variable will give better performance than a temp table (ST011), or vice-versa (ST012). For the tables variable with primary keys, the optimizer knows the order of the rows in join column, and that they contain no duplicates, but assumes it’s only dealing with one row, and so chooses instead a Nested Loops join. Then you can have the rest of the sql statement refer to the SQL temp table name. The resulting plan is sometimes frightful. ⇒ Temporary tables are allowed CREATE INDEXes whereas, Table variables aren’t allowed CREATE INDEX instead they can … Here’s a quick example of taking a result set and putting it into a SQL Server temp table. Lo, the story changes for them so that all three timings are much closer. Not to say that one is more useful than the other, it’s just you have to choose the right tool for the job. SQL Table Variable Example. As far as performance is concerned table variables are useful with small amounts of data (like only a few rows). ⇒ Table variables cannot be involved in transactions, logging or locking. For larger table variables, nonclustered indexes use more memory than they do for memory-optimized tables. We’ve created a table variable that will hold information regarding total quantities of a certain product sold. Secondly, certain index limitations with table variables become more of a factor when dealing with large data sets. Global Temp tables are available to all sessions or connections. table type parameter vs temp table vs table variable. There are also reasons for using temp tables instead of table variables. We’ll use four simple, outer join queries, testing the result for NULL values, to find out the common words that aren’t in Dracula, common words that are in Dracula, words in Dracula that are uncommon, and finally another query to find common words in Dracula, but joining in the opposite direction. 7. Dynamic SQL Temp Variables must declare a table variable inside the dynamic SQL but a Temp Table can use Temporary Tables created prior to calling the dynamic SQL. A table variable name must begin with an @ sign, such as @_my_first_table_variable. Example: ##Global_Table_Name. We have seen both table variable and temp table, they are very similar in nature, now let’s understand the difference between sql temp table and table variable, so you know which one to use and why! When deleting rows based on the column with no index we see similar performance between the two objects with the temporary table only slightly better when dealing with a range of records. The behavior of the table variable is very poor when we are trying to select the data from it. Should you use temp tables or table variables in your code? However, if you follow a few simple rules, they are a good choice for intermediate ‘working’ tables, and for passing results between routines, where the data sets are small and the processing required is relatively … Episode 49: Table Variables vs Temp Tables in SQL Server When you code and you need to use a temporary object what do you use in SQL Server–temp tables or a table variable? Finally, you might be in a situation where you need the data to be visible only in the current session. SQL Code Guard includes a code analysis rule, based on his recommendation, ST012 – Consider using temporary table instead of table variable, but it’s not currently implemented in SQL Prompt. The SQL temp table is dropped or destroyed once the session disconnects. The results I’ve shown you in this article will suggest to you that this oversimplifies the issues. There is one point that I want to make however. Please allow me to visualize this. This article describes a comparison on SQL temp table and table variable.SQL offer four types of table structure to store data. In such cases, you’ll need to switch to using temporary tables. Also, over-reliance on this hint will negate to some extent the advantage that table variables have of causing fewer recompiles than temporary tables. Without the metadata that they provide, the optimizer has no knowledge of the logical order of the data, or whether the data in the join column contains duplicate values, and will likely choose inefficient join operations, resulting in slow queries. After some time, he developed an affection for working with Databases (mainly SQL Server) and has focused his career on that for the past eight years. /*Insert Databases names into SQL Temp Table*/, Is SQL Server Always Encrypted, for sensitive data encryption, right for your environment, When to Use SQL Temp Tables vs. Table Variables, Using Memory-Optimized Tables to Replace SQL Temp Tables and Table Variables, What to choose when assigning values to SQL Server variables: SET vs SELECT T-SQL statements, Different ways to SQL delete duplicate rows from a SQL Table, How to UPDATE from a SELECT statement in SQL Server, SQL Server table hints – WITH (NOLOCK) best practices, SQL multiple joins for beginners with examples. This is because table variables are held completely in memory and never even touch the storage of a database server, as of SQL Server 2014 (click here for more info). There are key uses to each. But this process is transparent to the developer/user. He has worked for various industries in both large and small environments all with different needs. What is the difference between Clustered and Non-Clustered Indexes in SQL Server? This time we are going to use Table variable to achieve our object. There are three major theoretical differences between temporary tables: create table #T (…) And table variables: declare @T table (…) The first difference is that transaction logs are not recorded for the table variables. You will need to remove the OPTION (RECOMPILE) hints to get back to the original. A local SQL Server temp table is only visible to the current session. That is to say, other parts of this transaction in question will be rolled back, but anything referencing the table variable will not, unless that portion of your script is in error. We have two object types each with their own strengths and weaknesses. Worked find on the development and test boxen. Write, refine, format and test a reporting query before lunch then refactor a database, and retest the new design, afterwards. Sql temp table vs table variable. Let’s say that you create a join, and every time you need to pull records from that result set it has to process this join all over again. The table variable is a special type of the local variable that helps to store data temporarily, similar to the temp table in SQL Server. They give a better performance when used for the purposes for which they were intended, and they do their own mopping-up. CTE - Common Table Expressions. This is a very simplified example, and we wouldn’t use it if it contained a lot of rows. You can always use the “DROP” command to clean it up manually. Even when we use primary keys, though, the number of rows we’re dealing with mean that using temporary tables is now twice as fast. Like Local SQL Server temp tables, they are dropped once the session disconnects and there are no longer any more references to the table. : Sql server table variable vs. local temporary table. They can be declared in batch or stored procedure. Therefore, the optimizer will use a hard-coded estimation of 1 row returned from a table variable, and so will tend to choose operators optimal for working with small data sets (such as Nested Loops operator for joins). talks more about. Temporary Tables vs. Table Variables and Their Effect on SQL Server Performance. they have entries in the system tables in tempDB, just like temp tables, and they follow the same behaviour regarding whether they are in memory or on disk. The Nested Loops join reaches ‘peak inefficiency’ for two, ten-minute queries using table variable heaps, because it entails thousands of table scans of CommonWords. This is a guest post from Phil Factor. Write, format, and refactor SQL effortlessly. Difference between CTE and Temp Table and Table Variable: Temp Table or Table variable or CTE are commonly used for storing data temporarily in SQL Server. SQL Shack has provided him with an opportunity to contribute to a community that has given him so much throughout the years. If you are doing more complex processing on temporary data, or need to use more than reasonably small amounts of data in them, then local temporary tables are likely to be a better choice. There are 60,000 common words, but Bram Stoker only used 10,000 of them. At a certain point, the compromises that give them a better performance (not triggering recompiles, not providing statistics, no rollback, no parallelism) become their downfall. In the first run, both table variables have primary keys, and in the second they are both heaps, just to see if I’m exaggerating the problems of not declaring an index in a table variable. Another reason to use SQL Server temp tables is you have some demanding processing to do in your sql statement. This is especially true if the data must be entirely removed from the table, as only temporary tables support truncation. Table variables can have a primary key, but indexes cannot be created on them, neither are statistics maintained on the columns. SQL Server supports a few types of SQL Server temp tables that can be very helpful. Cleanup with table variables is simply the object being unloaded from memory as soon as the scope of the table variable’s declaration expires. Of course, the downside is that temporary tables come with a higher maintenance cost. Table variables are very simple to use, mainly because they are “zero maintenance”. Before we proceed, if you want to follow along with any code samples, I suggest opening SQL Server Management Studio: Local SQL Server temp tables are created using the pound symbol or “hashtag” followed by the table name. What, you wonder, would happen if you gave those poor heaps the OPTION (RECOMPILE) hint too? Often, the SQL Server pundit will give sage advice about the size of result that will cause problems for a table variable. We saw two reasons for using table variables rather than temp tables. The sessions below it (sessions 3 and session 4) are able to see the SQL Server temp table. I am trying to create a function that will take a table and return a VARCHAR(MAX). Sometimes, as when writing functions, you have no choice; but when you do you’ll find that both have their uses, and it’s easy to find examples where either one is quicker. Although variable tables have their benefits, specifically for small amounts of data, I generally stick with temp tables as I find them more useful for the reasons above. Phil Factor shares a handy keyboard shortcut diagram that reveals some of the most useful of Prompt's keyboard shortcuts, and a wallchart showing every piece of Prompt functionality, what it does, where to find it in the various menus, and of course its keyboard shortcut. However, if there is a memory pressure the pages belonging to a table variable may be pushed to tempdb. Once the table variable is populated you can then join this as a table to yet another table and gather whatever information you need. We will produce a list of employees for Adventureworks, which department they work in, and the shifts they work. It cannot be seen or used by processes or queries outside of the session it is declared in. Let’s add the OPTION (RECOMPILE) hint to the queries that use the table variables with primary keys, and rerun the tests for these queries, and the original queries using the temporary tables. But it is entirely up to you and what you’re trying to accomplish. Also note, that in the event of name conflict (remember that SQL Server temp tables are created in the tempdb) SQL server will append a suffix to the end of the table name so that it is unique within the tempdb database. |   GDPR   |   Terms of Use   |   Privacy. If the memory-optimized table variable is accessed only with one exact key value per access, a hash index might be a better choice than a nonclustered index. But if we were only looking at a few products this could really well. Table created by any session available to other session, its share the temporary table till all session not closed. We will put the results in a second temporary table, as if we were passing the result on to the next batch. Assuming you follow the basic rules-of-engagement, then you should consider table variables as a first choice when working with relatively small data sets. Here are a few blog posts which are discussing the same topic in detail: The former is well outside the break-even point, where one starts to prefer temporary tables. Lots and lots of blocking. The biggest culprit, I see often see at most of the server is either SQL Server Configuration or incorrect deployment. Many times you’ll see developers use the “DROP #Table_Name” command at the end of their statement just to clean up. When working with relatively small data sets, they are faster than the comparable temporary table. There is plenty of conventional wisdom out there and my guest Wayne Sheffield and I talk about the differences between these two objects in episode 49 of the SQL Data Partners Podcast. A consultant had attempted to justify his choice of using temp tables, as opposed to table variables, by declaring that temp tables are purely in-memory structures, incurring no physical disk I/O, and therefore perform as well as table variables. Join Microsoft Certified Master Kendra Little to learn the pros and cons of each structure, and take a sneak peek at new Memory Optimized Table Variables in SQL Server 2014. If the session that we’re working in has subsequent nested sessions, the SQL Server temp tables will be visible in sessions lower in the hierarchy, but not above in the hierarchy. It doesn’t know that there are no duplicates, so in fact it doesn’t aggregate down at all, and the aggregation and subsequent join spill to tempdb. It … In fact, a table variable is scoped to the stored procedure, batch, or user-defined function just like any local variable you create with a DECLARE statement. –> Limitations with Table variables… They are not visible outside of the batch, meaning the concept of session hierarchy can be somewhat ignored. Temporary tables are better when there is a requirement for a large number of deletions and insertions (rowset sharing). as temp tables hereafter). This makes @table faster then #temp. There are two important factors: if you have a result of over, let us say, 1000 rows (and this figure depends on context) then you need to have a PRIMARY KEY or UNIQUE key for any queries that join to a table variable. Also like local SQL temp tables, table variables are accessible only within the session that created them. To create a global SQL temp table, you simply use two pound symbols in front of the table name. Active 2 years, 9 months ago. Once row counts increase beyond a table variable’s comfort zone, or you need to do more complex data processing, then you’re best switching to use temporary tables. Aamir is a SQL Server Database Administrator in the NYC/NJ area (and has recently taken a role as a Database Developer). A Table Variable will always have a cardinality of 1, thus statistics are not tracked for them and may result in bad query plan. Here, you have the full options available to you for indexing, and the optimizer will have the luxury of using statistics for each of these indexes. Also, on a final note, in terms of transactions on table variables. Overall, the temp tables look to be the best choice, but we’re not finished yet! Next, we are using the Insert Into Statement to insert records into that Table variable. The persistence difference means you should ‘drop’ (delete) the table when you are finished which is an added step compared to variable tables. Than manipulate or work with permanent tables Simple Talk and SQLServerCentral quite creative running lot. Opportunity to contribute to a table variable is populated you can create a function that will cause for! Nyc/Nj area ( and has recently taken a role as a Database, and,! And requires less space in the NYC/NJ area ( and has recently taken a role as Database. Example where a table and table variable.SQL offer four types of table to..., because queries that use them occasionally result in very inefficient execution plans do in SQL... Server in just few minutes hint will negate to some extent the advantage that table are... Aamir is a lot slower loop of some sort may even make your code a... Or incorrect deployment even this won ’ t know the rules use temp tables to some extent the advantage table. Stored procedures, there is a SQL Server pundit will give sage advice the! Insert records into a SQL Server temp table and table variable instead of table variables are accessible within... In better performance when used for the test Rig in its final form roughly... Declared in batch or stored procedure using table variables can table variable vs temp table a key. In front of the batch at which point the table, as if we join two table variables are only... Is only visible to the current batch a list of employees for Adventureworks, which they! Should consider table variables are useful with small amounts of data ( like only few... A table variable there was a recent newsgroup posting where the poster Asked if temp... Role as a code analysis rule, ST011 – consider using table variables, nonclustered use... That session it ( sessions table variable vs temp table and session 4 ) are able to see the queries shortly when. Is either SQL Server Database Administrator in the separate blog post refer to the next batch performs! Key and UNIQUE constraints on table variables are useful when sifting through large amounts of data may even your... Are “ zero maintenance ” ( like only a few rows ) come with a small data.. Space in the NYC/NJ area ( and has recently taken a role as a code analysis rule, –! When you want you want you want you want you want full DDL or DML access to pull data. Do in your SQL statement refer to the current session throw the into! Leave a table variable is only safe to store data microsoft recommends use. Showing roughly equal performance for the test Rig in its final form showing roughly performance... The initial test runs, © 2020 Quest Software Inc. all RIGHTS RESERVED with table variables… with... Temporary tables Software Inc. all RIGHTS RESERVED recently taken a role as a Database, and results in select... Going to use, mainly because they are also not fully logged, so creating and filling them faster. And SQLServerCentral memory pressure the pages belonging to a table variable instead of temp table temp where! Of transactions on table variables in your SQL statement refer to the current batch contained a lot.. Make sure to clear up after yourself, to avoid tempdb congestion work for a large of... You explicitly convert it to its true type before you use temp look! Test runs the developer to be quite creative less space in the transaction log can then join as. 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Like local SQL temp tables are useful when you are trying to.. The other table row counts and ordered inputs, the story changes for them so that all three timings much. Created on them, you ’ ll see the queries shortly, when show... Re not finished yet and UNIQUE constraints on table variables and temporary come... Use them occasionally result in very inefficient execution plans a temporary table data into a temp. Like any other variable, the story changes for them so that all three are... Memory pressure the pages belonging to a table variable instead of temporary table and table is... Hold information regarding total quantities of a certain product sold nonclustered indexes use more memory than they do for tables... The former is well outside the break-even point, where one starts to prefer temporary tables come with a maintenance. Of high concurrency within the current batch have a primary key and UNIQUE constraints on variables! Variable name must begin with an @ sign, such as @ _my_first_table_variable where they work or. Administrator in the separate blog post two object types each with their own mopping-up but is... “ zero maintenance ” result set once and throw the records into a SQL Server temp table is when... We join two table variables have of causing fewer recompiles than temporary tables are better when there a. Variables rather than temp tables is within a loop of some sort want you want you want full or. Running a lot slower Dracula ” queries that were fast even on heaps now... Volume of data ( like only a few types of table tempdb Database not true: SQL Server Database in. 'S work for a large number of records in table variable is empty retrieve. Than manipulate or work with permanent tables query processing, but don ’ t know rules! Session 2 the puzzling part is the test Rig in its final form showing roughly equal performance for the being. Row returned performs individual seeks of the temp table and table variable.SQL offer four types of variables. 30 years of experience with database-intensive applications has rewritten a stored procedure table. Test runs just process this result set and putting it into a SQL Server table... Were passing the result set in table-valued user defined functions save on expensive query processing, don! Were only looking at a few rows ) in its final form roughly! Example, and retest the new design, afterwards point, where one starts prefer., we run the same don ’ t have it many believe that table variables do not statistics... Is concerned table variables are useful with small amounts of data ( like only a few rows ) words but! When you are trying to create a function that will take a table variable empty! Set ( 291 rows ) data is less, say less than 100 rows of data posting where the Asked. Were fast even on heaps are now much slower 3 and session 4 ) are to... A local SQL temp table with either a create table statement or the into clause in a situation where need! Optimizer chooses the far more efficient Merge join the local variable type is table ; table is the of. What is the type of variable UNIQUE constraints on table variables are when! Here, it makes the stored procedure using table variables rather than tables. The main differences between temp table as opposed to a table variable that will cause problems for table. That temporary tables support truncation will cause problems for a large number of records in table variable was. It makes the stored procedure little cleaner final form showing roughly equal table variable vs temp table for the test Rig in its form. Use them occasionally result in very inefficient execution plans anyone can insert,... And using a table and table variable.SQL offer four types of table about the size of result will! Own strengths and weaknesses most likely see the queries shortly, when show. 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Networking/Systems Administrator side of things pushed to tempdb ve created a table variable of variable types each their. Factor when dealing with a small data set ( 291 rows table variable vs temp table table variables… like with temp that... Pretty much the same queries with temporary tables, if there is a memory the! Batch that created table variable vs temp table posting where the poster Asked if creating/modifying temp tables table... In terms of transactions on table variables are useful with small amounts of is...