The Table Variable in SQL Server
- Definition. 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.
- Syntax. ...
- Transactions and table variable in SQL Server. ...
- Some useful tips for the table variables. ...
- Conclusion. ...
Full Answer
What are the types of variables in SQL Server?
- Numeric data types such as int, tinyint, bigint, float, real etc.
- Date and Time data types such as Date, Time, Datetime etc.
- Character and String data types such as char, varchar, text etc.
- Unicode character string data types, for example nchar, nvarchar, ntext etc.
- Binary data types such as binary, varbinary etc.
How do you declare a table variable in SQL?
The Table Variable in SQL Server
- Definition. 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.
- Syntax. ...
- Transactions and table variable in SQL Server. ...
- Some useful tips for the table variables. ...
- Conclusion. ...
How to check table variable is empty in SQL Server?
create table TestTable (id int) if object_id ('TestTable','U') is not null. drop table TestTable. Code. Database developers can read SQL tutorial DROP Table If Table Exists Command on a SQL Server Database for methods used to test the existence of a database table on SQL Server.
How do I set a variable in SQL?
- Add Variable: Adds a user-defined variable.
- Delete Variable: Deletes the selected user-defined variable.
- Show System Variables: Toggles between a list that includes system variables and one that does not. ...
What is variable table in SQL Server?
Definition. 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. 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.
What is a variable in a table?
Table variables are the variables selected on the Table tab for display in your output tables. Table variables are displayed by their groupings. For example, the Sex variable is displayed by the three groupings 'Male', 'Female', and 'Male and Female'.
What is table variable and temp table?
Table variable involves the effort when you usually create the normal tables. Temp table result can be used by multiple users. Table variable can be used by the current user only. Temp table will be stored in the tempdb. It will make network traffic.
How do you DECLARE a table variable in SQL?
To declare a table variable, you use the DECLARE statement as follows:DECLARE @table_variable_name TABLE ( column_list ); ... DECLARE @product_table TABLE ( product_name VARCHAR(MAX) NOT NULL, brand_id INT NOT NULL, list_price DEC(11,2) NOT NULL );More items...
Where is table variable stored in SQL Server?
It is stored in the tempdb system database. The storage for the table variable is also in the tempdb database. We can use temporary tables in explicit transactions as well. Table variables cannot be used in explicit transactions.
Which is better temp table or table variable in SQL Server?
As far as performance is concerned table variables are useful with small amounts of data (like only a few rows). Otherwise a SQL Server temp table is useful when sifting through large amounts of data. So for most scripts you will most likely see the use of a SQL Server temp table as opposed to a table variable.
What is the difference between temporary table and table variable in SQL?
Temporary Tables are physically created in the tempdb database. These tables act as the normal table and also can have constraints, index like normal tables. Table Variable acts like a variable and exists for a particular batch of query execution. It gets dropped once it comes out of batch.
What is difference between CTE and table variable?
This biggest difference is that a CTE can only be used in the current query scope whereas a temporary table or table variable can exist for the entire duration of the session allowing you to perform many different DML operations against them.
Are table variables better than temp tables?
Summary of Performance Testing for SQL Server Temp Tables vs. Table Variables. As we can see from the results above a temporary table generally provides better performance than a table variable. The only time this is not the case is when doing an INSERT and a few types of DELETE conditions.
How do I change the table variable in SQL Server?
DECLARE @TableName varchar(128) SET @TableName = 'Cases' DECLARE @sqlcmd VARCHAR(MAX) SET @sqlcmd = 'ALTER TABLE ' + QUOTENAME(@TableName) + ' ALTER COLUMN [CreatedBy] varchar(256);'; EXEC (@sqlcmd); SET @sqlcmd = 'ALTER TABLE ' + QUOTENAME(@TableName) + ' ALTER COLUMN [LastUpdatedBy] varchar(256);'; EXEC (@sqlcmd);
Does table variable use tempdb?
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).
Can table variables have indexes?
Short answer: Yes. A more detailed answer is below. Traditional tables in SQL Server can either have a clustered index or are structured as heaps. Clustered indexes can either be declared as unique to disallow duplicate key values or default to non unique.
How to declare a table variable?
How to declare table variables. To declare a table variable, you use the DECLARE statement as follows: In this syntax, you specify the name of the table variable between the DECLARE and TABLE keywords. The name of the table variables must start with the @ symbol. Following the TABLE keyword, you define the structure of the table variable which is ...
What is the scope of table variables?
The scope of table variables. Similar to local variables, table variables are out of scope at the end of the batch. If you define a table variable in a stored procedure or user-defined function, the table variable will no longer exist after the stored procedure or user-defined function exits.
Do table variables live in tempDB?
Similar to the temporary table, the table variables do live in the tempdb database, not in the memory.
Can you alter a table variable after it is declared?
First, you have to define the structure of the table variable during the declaration. Unlike a regular or temporary table, you cannot alter the structure of the table variables after they are declared.
Can you use table variables as input?
Third, you cannot use the table variable as an input or output parameter like other data types. However, you can return a table variable from a user-defined function. Fourth, you cannot create non-clustered indexes for table variables. However, starting with SQL Server 2014, memory-optimized table variables are available with the introduction ...
What is table variable?
Table variables are a special part of the local variable that allows us to hold complete table records temporarily. They are similar to the temporary tables in SQL Server. It is first introduced by Microsoft in SQL Server 2000 as an alternative for temp tables. Usually, the table variable supports all the properties of a local variable, ...
How many columns are in a table variable in SQL Server?
The below example declares a table variable named @months_table, which consists of three columns: number, month, and name:
What is stored procedure in SQL?
A stored procedure is a group of one or more pre-compiled SQL statements into a logical unit. Each procedure in SQL Server always contains a name, parameter lists, and Transact-SQL statements. The following example will explain how we can use table variables in stored procedures.
What is a user defined function?
A function defined by a user to perform a certain specific task is referred to as user-defined functions. A user will create this type of function for his own requirements. The following example will explain how we can use table variables in user-defined functions.
When are table variables cleaned up?
table variables are automatically cleaned up at the end of the function, stored procedure, or batch in which they're defined . table variables that are used in stored procedures cause fewer stored procedure recompilations than when temporary tables are used when there are no cost-based choices that affect performance.
What is table_type_definition#N#?
table_type_definition#N#Is the same subset of information that is used to define a table in CREATE TABLE. The table declaration includes column definitions, names, data types, and constraints. The only constraint types allowed are PRIMARY KEY, UNIQUE KEY, and NULL.#N#For more information about the syntax, see CREATE TABLE (Transact-SQL), CREATE FUNCTION (Transact-SQL), and DECLARE @local_variable (Transact-SQL).
Which is better: temp tables or RECOMPILE?
Temp tables may be a better solution in this case. For queries that join the table variable with other tables, use the RECOMPILE hint, which will cause the optimizer to use the correct cardinality for the table variable. table variables aren't supported in the SQL Server optimizer's cost-based reasoning model.
When should temporary tables be used?
Temporary tables are preferred when cost-based choices are required . This plan typically includes queries with joins, parallelism decisions, and index selection choices.
Can indexes be created on table variables?
Indexes can't be created explicitly on table variables, and no statistics are kept on table variables. Starting with SQL Server 2014 (12.x), new syntax was introduced which allows you to create certain index types inline with the table definition.
Can a table variable be used in SQL?
Within its scope, a table variable can be used like a regular table. It may be applied anywhere a table or table expression is used in SELECT, INSERT, UPDATE, and DELETE statements. However, table can't be used in the following statement: SQL. SELECT select_list INTO table_variable;
Do table variables have distribution statistics?
Table variables don't have distribution statistics. They won't trigger recompiles. In many cases, the optimizer will build a query plan on the assumption that the table variable has no rows. For this reason, you should be cautious about using a table variable if you expect a larger number of rows (greater than 100). Temp tables may be a better solution in this case. For queries that join the table variable with other tables, use the RECOMPILE hint, which will cause the optimizer to use the correct cardinality for the table variable.
What is @@ in SQL?
Although in earlier versions of SQL Server, the @@functions are referred to as global variables, @@functions aren't variables, and they don't have the same behaviors as variables. The @@functions are system functions, and their syntax usage follows the rules for functions.
What is scope in SQL?
The scope of a variable is the range of Transact-SQL statements that can reference the variable. The scope of a variable lasts from the point it is declared until the end of the batch or stored procedure in which it is declared.
Can a variable have a value?
A variable can also have a value assigned by being referenced in a select list. If a variable is referenced in a select list, it should be assigned a scalar value or the SELECT statement should only return one row. For example: SQL.
Does SQL Server guarantee the order of evaluation of the expressions?
If there are multiple assignment clauses in a single SELECT statement, SQL Server does not guarantee the order of evaluation of the expressions. Note that effects are only visible if there are references among the assignments.
Can @@functions be variables?
Although in earlier versions of SQL Server, the @@functions are referred to as global variables, @@functions aren't variables, and they don't have the same behaviors as variables. The @@functions are system functions, and their syntax usage follows the rules for functions. You can't use variables in a view.
Can you use variables in a view?
You can't use variables in a view. Changes to variables aren't affected by the rollback of a transaction. The following script creates a small test table and populates it with 26 rows. The script uses a variable to do three things: Control how many rows are inserted by controlling how many times the loop is executed.
Introduction
Most of us have heard this question from the software developers who are familiar with SQL Server:
User-defined table types
User-defined table types are the predefined tables that the schema definition is created by the users and helps to store temporary data. User-defined table types support primary keys, unique constraints and default values, etc.
Using Table-Valued Parameters in Stored Procedures
TVPs reference their types from the user-defined table so they inherit the schema of the table. In this way, we can obtain a parameter that can transfer the multiple columns and rows into the stored procedure as input.
Using Memory-Optimized Table-Valued Parameters
In-memory OLTP, objects can provide an advantage to improve the performance of the queries. In this context, memory-optimized tables can enable us with more effective data access. Moving from this idea, it seems possible to create memory-optimized TVPs. The main advantage of using memory-optimized TVPs is minimizing tempdb activity.
Monitoring tempdb activity of the Table-Valued Parameters
We mentioned that memory-optimized TVPs do not show activity on the tempdb database. In this part, we will prove this concept. At first, we will launch the performance monitor and clear all existing counters with the delete key.
Conclusion
In this article, we learned about the Table-Valued Parameter usage details and we also mentioned memory-optimized TVPs performance issues. At this point, we will have to decide which TVP type provides maximum benefit according to the resource consumption and performance balance.
See more
Esat Erkec is a SQL Server professional who began his career 8+ years ago as a Software Developer. He is a SQL Server Microsoft Certified Solutions Expert.
Syntax
- The following syntax describes how to declare a table variable: If we want to declare a table variable, we have to start the DECLARE statement which is similar to local variables. The name of the local variable must start with at(@) sign. The TABLE keyword specifies that this variable is a …
What Is The Storage Location of The Table variables?
- The answer to this question is – table variables are stored in the tempdb database. Why we underline this is because sometimes the answer to this question is that the table variable is stored in the memory, but this is totally wrong. Before proving the answer to this question, we should clarify one issue about the table variables. The lifecycle of the table variables starts in the declar…
How Can We Use Constraints with The Table variables?
- Constraints are database objects that ensure data integrity. Table variables allow us to create the following constraints: 1. Primary Key 2. Unique 3. Null 4. Check In the following example, we will successfully use all types of constraints on the table variable seamlessly: On the other hand, Foreign Key constraints cannot use for the table variables. The other restriction is, we have to de…
Transactions and Table Variable in SQL Server
- Transactions are the smallest logical unit that helps to manage the CRUD(insert, select, update and delete) operations in the SQL Server. Explicit transactions are started with BEGIN TRAN statement and they can be completed with COMMIT or ROLLBACK statements. Now we will execute the following query and then analyze the result: Table variable CRUD operations do not …
Some Useful Tips For The Table Variables
- TRUNCATE statement does not work for table variables
The TRUNCATE statement helps to delete all rows in the tables very quickly. However, this statement cannot be used for table variables. For example, the following query will return an error: - The table variable structure cannot be changed after it has been declared
According to this tip interpretation, the following query has to return an error:
Conclusion
- In this article, we explored the table variable in SQL Server details with various examples. Also, we mentioned the features and limitations of the table variables.
What Are Table Variables
How to Declare Table Variables
- To declare a table variable, you use the DECLAREstatement as follows: In this syntax, you specify the name of the table variable between the DECLARE and TABLE keywords. The name of the table variables must start with the @symbol. Following the TABLEkeyword, you define the structure of the table variable which is similar to the structure of a regular table that includes column definiti…
The Scope of Table Variables
- Similar to local variables, table variables are out of scope at the end of the batch. If you define a table variable in a stored procedure or user-defined function, the table variable will no longer exist after the stored procedure or user-defined function exits.
Table Variable Example
- For example, the following statement declares a table variable named @product_table which consists of three columns: product_name, brand_id, and list_price:
Restrictions on Table Variables
- First, you have to define the structure of the table variable during the declaration. Unlike a regular or temporary table, you cannot alterthe structure of the table variables after they are declared. Second, statistics help the query optimizer to come up with a good query’s execution plan. Unfortunately, table variables do not contain statistics. Therefore, you should use table variable…
Performance of Table Variables
- Using table variables in a stored procedure results in fewer recompilations than using a temporary table. In addition, a table variable use fewer resources than a temporary table with less locking and logging overhead. Similar to the temporary table, the table variables do live in the tempdbdatabase, not in the memory.
Using Table Variables in User-Defined Functions
- The following user-defined function named ufnSplit()that returns a table variable. The following statement calls the udfSplit()function: Here is the output: In this tutorial, you will learn how to use the SQL Server table variables which offer some performance benefits and flexibility in comparison with temporary tables.