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SELECT @local_variable (Transact-SQL)

Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance Azure Synapse Analytics SQL analytics endpoint in Microsoft Fabric Warehouse in Microsoft Fabric SQL database in Microsoft Fabric

Sets a local variable to the value of an expression.

For assigning variables, use SET @local_variable instead of SELECT @local_variable.

Transact-SQL syntax conventions

Syntax

SELECT { @local_variable { = | += | -= | *= | /= | %= | &= | ^= | |= } expression }
    [ , ...n ] [ ; ]

Arguments

@local_variable

A declared variable for which you assign a value.

{ = | += | -= | *= | /= | %= | &= | ^= | |= }

Assign the value on the right to the variable on the left.

Compound assignment operator:

Operator Action
= Assigns the expression that follows, to the variable.
+= Add and assign
-= Subtract and assign
*= Multiply and assign
/= Divide and assign
%= Modulo and assign
&= Bitwise AND and assign
^= Bitwise XOR and assign
|= Bitwise OR and assign

expression

Any valid expression. This term includes a scalar subquery.

Remarks

Use SELECT @local_variable to return a single value into the variable. However, when expression is the name of a column, it can return multiple values. If the SELECT statement returns more than one value, the variable gets the last value that the query returns.

If the SELECT statement returns no rows, the variable keeps its current value. If expression is a scalar subquery that returns no value, the variable is set to NULL.

One SELECT statement can initialize multiple local variables.

Note

You can't use a SELECT statement that contains a variable assignment to also perform typical result set retrieval operations.

Examples

The code samples in this article use the AdventureWorks2025 or AdventureWorksDW2025 sample database, which you can download from the Microsoft SQL Server Samples and Community Projects home page.

The AdventureWorksLT database is used as the sample database for Azure SQL Database.

A. Use SELECT @local_variable to return a single value

In the following example, the variable @var1 gets the value 'Generic Name'. The query against the Store table returns no rows because the value specified for CustomerID doesn't exist in the table. The variable keeps the "Generic Name" value.

DECLARE @var1 AS VARCHAR (30);

SELECT @var1 = 'Generic Name';

SELECT @var1 = [Name]
FROM SalesLT.Product
WHERE ProductID = 1000000;

SELECT @var1 AS 'ProductName';

Here's the result set.

ProductName
------------------------------
Generic Name

B. Use SELECT @local_variable to return null

In the following example, a subquery assigns a value to @var1. Because the value requested for CustomerID doesn't exist, the subquery returns no value, and the variable is set to NULL.

DECLARE @var1 AS VARCHAR (30);

SELECT @var1 = 'Generic Name';

SELECT @var1 = (SELECT [Name]
                FROM SalesLT.Product
                WHERE ProductID = 1000000);

SELECT @var1 AS 'Company Name';

Here's the result set.

Company Name
----------------------------
NULL

C. Antipattern use of recursive variable assignment

Avoid the following pattern for recursive use of variables and expressions:

SELECT @Var = <expression containing @Var>
FROM
...

In this case, it isn't guaranteed that @Var is updated on a row by row basis. For example, @Var might be set to initial value of @Var for all rows. This behavior occurs because the order and frequency in which the assignments are processed is nondeterminant. This rule applies to expressions containing variables string concatenation, as demonstrated in the following example, but also to expressions with non-string variables or += style operators. Use aggregation functions instead for a set-based operation instead of a row-by-row operation.

For string concatenation, consider the STRING_AGG function, introduced in SQL Server 2017 (14.x), for scenarios where ordered string concatenation is desired. For more information, see STRING_AGG.

The following example shows an antipattern to avoid. Using ORDER BY in an attempt to order concatenation causes the list to be incomplete:

DECLARE @List AS NVARCHAR (MAX);

SELECT @List = CONCAT(COALESCE (@List + ', ', ''), p.LastName)
FROM Person.Person AS p
WHERE p.FirstName = 'William'
ORDER BY p.BusinessEntityID;

SELECT @List;

Here's the result set.

(No column name)
---
Walker

Instead, consider:

DECLARE @List AS NVARCHAR (MAX);

SELECT @List = STRING_AGG(p.LastName, ', ') WITHIN GROUP (ORDER BY p.BusinessEntityID)
FROM Person.Person AS p
WHERE p.FirstName = 'William';

SELECT @List;

Here's the result set.

(No column name)
---
Vong, Conner, Hapke, Monroe, Richter, Sotelo, Vong, Ngoh, White, Harris, Martin, Thompson, Martinez, Robinson, Clark, Rodriguez, Smith, Johnson, Williams, Jones, Brown, Davis, Miller, Moore, Taylor, Anderson, Thomas, Lewis, Lee, Walker

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