SET @local_variable (Transact-SQL)

Artikkeli
11/20/2023

Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance Azure Synapse Analytics Analytics Platform System (PDW) SQL analytics endpoint in Microsoft Fabric Warehouse in Microsoft Fabric SQL database in Microsoft Fabric

Sets the specified local variable, previously created by using the DECLARE @local_variable statement, to the specified value.

Transact-SQL syntax conventions

Syntax

Syntax for SQL Server, Azure SQL Database, and Azure SQL Managed Instance:

SET
{ @local_variable
    [ . { property_name | field_name } ] = { expression | udt_name { . | :: } method_name }
}
| { @SQLCLR_local_variable.mutator_method }
| { @local_variable
    { += | -= | *= | /= | %= | &= | ^= | |= } expression
}
| { @cursor_variable =
    { @cursor_variable | cursor_name
    | { CURSOR [ [ LOCAL | GLOBAL ] ]
        [ FORWARD_ONLY | SCROLL ]
        [ STATIC | KEYSET | DYNAMIC | FAST_FORWARD ]
        [ READ_ONLY | SCROLL_LOCKS | OPTIMISTIC ]
        [ TYPE_WARNING ]
    FOR select_statement
        [ FOR { READ ONLY | UPDATE [ OF column_name [ , ...n ] ] } ]
      }
    }
}

Syntax for Azure Synapse Analytics and Parallel Data Warehouse and Microsoft Fabric:

SET @local_variable { = | += | -= | *= | /= | %= | &= | ^= | |= } expression

Arguments

@local_variable

The name of a variable of any type except cursor, text, ntext, image, or table. Variable names must start with one at sign (@). Variable names must follow the rules for identifiers.

property_name

A property of a user-defined type.

field_name

A public field of a user-defined type.

udt_name

The name of a common language runtime (CLR) user-defined type.

{ . | :: }

Specifies a method of a CLR user-define type. For an instance (non-static) method, use a period (.). For a static method, use two colons (::). To invoke a method, property, or field of a CLR user-defined type, you must have EXECUTE permission on the type.

method_name ( argument [ ,... n ] )

A method of a user-defined type that takes one or more arguments to modify the state of an instance of a type. Static methods must be public.

@SQLCLR_local_variable

A variable whose type is located in an assembly. For more information, see Common language runtime (CLR) integration programming concepts.

mutator_method

A method in the assembly that can change the state of the object. SQLMethodAttribute.IsMutator is applied to this method.

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

Compound assignment operator:

+= - 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.

cursor_variable

The name of a cursor variable. If the target cursor variable previously referenced a different cursor, that previous reference is removed.

cursor_name

The name of a cursor declared by using the DECLARE CURSOR statement.

CURSOR

Specifies that the SET statement contains a declaration of a cursor.

SCROLL

Specifies that the cursor supports all fetch options: FIRST, LAST, NEXT, PRIOR, RELATIVE, and ABSOLUTE. You can't specify SCROLL when you also specify FAST_FORWARD.

FORWARD_ONLY

Specifies that the cursor supports only the FETCH NEXT option. The cursor is retrieved only in one direction, from the first to the last row. When you specify FORWARD_ONLY without the STATIC, KEYSET, or DYNAMIC keywords, the cursor is implemented as DYNAMIC. If you don't specify either FORWARD_ONLY or SCROLL, FORWARD_ONLY is the default, unless you specify the keywords STATIC, KEYSET, or DYNAMIC. For STATIC, KEYSET, and DYNAMIC cursors, SCROLL is the default.

STATIC

Defines a cursor that makes a temporary copy of the data to be used by the cursor. All requests to the cursor are answered from this temporary table in tempdb. As a result, modifications made to the base tables after the cursor is opened aren't reflected in the data returned by fetches made to the cursor. And, this cursor doesn't support modifications.

KEYSET

Specifies that the membership and order of rows in the cursor are fixed when the cursor is opened. The set of keys that uniquely identify the rows is built into the keysettable in tempdb. Changes to nonkey values in the base tables, either made by the cursor owner or committed by other users, are visible as the cursor owner scrolls around the cursor. Inserts made by other users aren't visible, and inserts can't be made through a Transact-SQL server cursor.

If a row is deleted, an attempt to fetch the row returns a @@FETCH_STATUS of -2. Updates of key values from outside the cursor are similar to a delete of the old row followed by an insert of the new row. The row with the new values isn't visible, and tries to fetch the row with the old values return a @@FETCH_STATUS of -2. The new values are visible if the update happens through the cursor by specifying the WHERE CURRENT OF clause.

DYNAMIC

Defines a cursor that reflects all data changes made to the rows in its result set as the cursor owner scrolls around the cursor. The data values, order, and membership of the rows can change on each fetch. The absolute and relative fetch options aren't supported with dynamic cursors.

FAST_FORWARD

Specifies a FORWARD_ONLY, READ_ONLY cursor with optimizations enabled. FAST_FORWARD can't be specified when SCROLL is also specified.

READ_ONLY

SCROLL LOCKS

Specifies that positioned updates or deletes made through the cursor are guaranteed to succeed. SQL Server locks the rows as they're read into the cursor to guarantee their availability for later modifications. You can't specify SCROLL_LOCKS when FAST_FORWARD is also specified.

OPTIMISTIC

Specifies that positioned updates or deletes made through the cursor don't succeed if the row was updated since being read into the cursor. SQL Server doesn't lock rows as they're read into the cursor. Instead, it uses comparisons of timestamp column values, or a checksum value, if the table has no timestamp column, to determine if the row was modified after being read into the cursor. If the row was modified, the attempted positioned update or delete fails. You can't specify OPTIMISTIC when FAST_FORWARD is also specified.

TYPE_WARNING

Specifies that a warning message is sent to the client when the cursor is implicitly converted from the requested type to another.

FOR select_statement

A standard SELECT statement that defines the result set of the cursor. The keywords FOR BROWSE, and INTO aren't allowed within the select_statement of a cursor declaration.

If you use DISTINCT, UNION, GROUP BY, or HAVING, or you include an aggregate expression in the select_list, the cursor is created as STATIC.

If each underlying table doesn't have a unique index and an ISO SCROLL cursor or if a Transact-SQL KEYSET cursor is requested, the cursor is automatically a STATIC cursor.

If select_statement contains an ORDER BY clause in which the columns aren't unique row identifiers, a DYNAMIC cursor is converted to a KEYSET cursor, or to a STATIC cursor if a KEYSET cursor can't be opened. This process also occurs for a cursor defined by using ISO syntax but without the STATIC keyword.

READ ONLY

Prevents updates from being made through this cursor. The cursor can't be referenced in a WHERE CURRENT OF clause in an UPDATE or DELETE statement. This option overrides the default capability of a cursor to be updated. This keyword varies from the earlier READ_ONLY by having a space instead of an underscore between READ and ONLY.

UPDATE [ OF column_name [ ,... n ] ]

Defines updatable columns within the cursor. If OF <column_name> [ , ...n ] is supplied, only the columns listed allow modifications. When no list is supplied, all columns can be updated, unless the cursor is defined as READ_ONLY.

Remarks

After a variable is declared, it's initialized to NULL. Use the SET statement to assign a value that isn't NULL to a declared variable. The SET statement that assigns a value to the variable returns a single value. When you initialize multiple variables, use a separate SET statement for each local variable.

You can use variables only in expressions, not instead of object names or keywords. To construct dynamic Transact-SQL statements, use EXECUTE.

Although syntax rules for SET @cursor_variable include the LOCAL and GLOBAL keywords, when you use the SET @cursor_variable = CURSOR... syntax, the cursor is created as GLOBAL or LOCAL, depending on the setting of the default to local cursor database option.

Cursor variables are always local, even if they reference a global cursor. When a cursor variable references a global cursor, the cursor has both a global and a local cursor reference. For more information, see Example D, Use SET with a global cursor.

For more information, see DECLARE CURSOR (Transact-SQL).

You can use the compound assignment operator anywhere you have an assignment with an expression on the right-hand side of the operator, including variables, and a SET in an UPDATE, SELECT, and RECEIVE statement.

Don't use a variable in a SELECT statement to concatenate values (that is, to compute aggregate values). Unexpected query results might occur because all expressions in the SELECT list (including assignments) aren't necessarily run exactly once for each output row. For more information, see KB 287515.

Permissions

Requires membership in the public role. All users can use SET @local_variable.

Examples

The Transact-SQL code samples in this article use the AdventureWorks2022 or AdventureWorksDW2022 sample database, which you can download from the Microsoft SQL Server Samples and Community Projects home page.

A. Print the value of a variable initialized by using SET

The following example creates the @myVar variable, puts a string value into the variable, and prints the value of the @myVar variable.

DECLARE @myVar CHAR(20);
SET @myVar = 'This is a test';
SELECT @myVar;
GO

B. Use a local variable assigned a value by using SET in a SELECT statement

The following example creates a local variable named @state and uses the local variable in a SELECT statement to find the first name (FirstName) and family name (LastName) of all employees who live in the state of Oregon.

USE AdventureWorks2022;
GO
DECLARE @state CHAR(25);
SET @state = N'Oregon';
SELECT RTRIM(FirstName) + ' ' + RTRIM(LastName) AS Name, City
FROM HumanResources.vEmployee
WHERE StateProvinceName = @state;
GO

C. Use a compound assignment for a local variable

The following two examples produce the same result. Each example creates a local variable named @NewBalance, multiplies it by 10, then displays the new value of the local variable in a SELECT statement. The second example uses a compound assignment operator.

/* Example one */
DECLARE @NewBalance INT;
SET @NewBalance = 10;
SET @NewBalance = @NewBalance * 10;
SELECT @NewBalance;
GO

/* Example Two */
DECLARE @NewBalance INT = 10;
SET @NewBalance *= 10;
SELECT @NewBalance;
GO

D. Use SET with a global cursor

The following example creates a local variable and then sets the cursor variable to the global cursor name.

DECLARE my_cursor CURSOR GLOBAL
FOR SELECT * FROM Purchasing.ShipMethod
DECLARE @my_variable CURSOR ;
SET @my_variable = my_cursor ;
--There is a GLOBAL cursor declared(my_cursor) and a LOCAL variable
--(@my_variable) set to the my_cursor cursor.

DEALLOCATE my_cursor;
GO
--There is now only a LOCAL variable reference
--(@my_variable) to the my_cursor cursor.

E. Define a cursor by using SET

The following example uses the SET statement to define a cursor.

DECLARE @CursorVar CURSOR;

SET @CursorVar = CURSOR SCROLL DYNAMIC
FOR
SELECT LastName, FirstName
FROM AdventureWorks2022.HumanResources.vEmployee
WHERE LastName like 'B%';

OPEN @CursorVar;

FETCH NEXT FROM @CursorVar;
WHILE @@FETCH_STATUS = 0
BEGIN
    FETCH NEXT FROM @CursorVar
END;

CLOSE @CursorVar;
DEALLOCATE @CursorVar;
GO

F. Assign a value from a query

The following example uses a query to assign a value to a variable.

USE AdventureWorks2022;
GO
DECLARE @rows INT;
SET @rows = (SELECT COUNT(*) FROM Sales.Customer);
SELECT @rows;
GO

G. Assign a value to a user-defined type variable by modifying a property of the type

The following example sets a value for user-defined type (UDT) Point by modifying the value of the property X of the type.

DECLARE @p Point;
SET @p.X = @p.X + 1.1;
SELECT @p;
GO

Learn more about creating the Point UDT referenced in this example and the following examples in the article Creating User-Defined Types.

H. Assign a value to a user-defined type variable by invoking a method of the type

The following example sets a value for user-defined type point by invoking method SetXY of the type.

DECLARE @p Point;
SET @p=point.SetXY(23.5, 23.5);

I. Create a variable for a CLR type and calling a mutator method

The following example creates a variable for the type Point, and then executes a mutator method in Point.

CREATE ASSEMBLY mytest FROM 'c:\test.dll' WITH PERMISSION_SET = SAFE
CREATE TYPE Point EXTERNAL NAME mytest.Point
GO
DECLARE @p Point = CONVERT(Point, '')
SET @p.SetXY(22, 23);

Examples: Azure Synapse Analytics and Analytics Platform System (PDW)

J. Print the value of a variable initialized by using SET