+= (String Concatenation Assignment) (Transact-SQL)
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
Concatenates two strings and sets the string to the result of the operation. For example, if a variable @x equals 'Adventure', then @x += 'Works' takes the original value of @x, adds 'Works' to the string, and sets @x to that new value 'AdventureWorks'.
Transact-SQL syntax conventions
Syntax
expression += expression
Arguments
expression
Is any valid expression of any of the character data types.
Result Types
Returns the data type that is defined for the variable.
Remarks
SET @v1 += 'expression' is equivalent to SET @v1 = @v1 + ('expression'). Also, SET @v1 = @v2 + @v3 + @v4 is equivalent to SET @v1 = (@v2 + @v3) + @v4.
The += operator cannot be used without a variable. For example, the following code will cause an error:
SELECT 'Adventure' += 'Works'
Examples
A. Concatenation using += operator
The following example concatenates using the +=
operator.
DECLARE @v1 VARCHAR(40);
SET @v1 = 'This is the original.';
SET @v1 += ' More text.';
PRINT @v1;
Here is the result set.
This is the original. More text.
B. Order of evaluation while concatenating using += operator
The following example concatenates multiple strings to form one long string and then tries to compute the length of the final string. This example demonstrates the evaluation order and truncation rules, while using the concatenation operator.
DECLARE @x VARCHAR(4000) = REPLICATE('x', 4000)
DECLARE @z VARCHAR(8000) = REPLICATE('z',8000)
DECLARE @y VARCHAR(max);
SET @y = '';
SET @y += @x + @z;
SELECT LEN(@y) AS Y; -- 8000
SET @y = '';
SET @y = @y + @x + @z;
SELECT LEN(@y) AS Y; -- 12000
SET @y = '';
SET @y = @y +(@x + @z);
SELECT LEN(@y) AS Y; -- 8000
-- or
SET @y = '';
SET @y = @x + @z + @y;
SELECT LEN(@y) AS Y; -- 8000
GO
Here is the result set.
Y
-------
8000
(1 row(s) affected)
Y
-------
12000
(1 row(s) affected)
Y
-------
8000
(1 row(s) affected)
Y
-------
8000
(1 row(s) affected)
See Also
Operators (Transact-SQL)
+= (Add Assignment) (Transact-SQL)
+ (String Concatenation) (Transact-SQL)