string-concatenation-equal-transact-sql.md

title	+= String concatenation
description	Concatenate two strings and set the string to the result of the operation.
titleSuffix	SQL Server (Transact-SQL)
ms.custom	seo-lt-2019
ms.date	12/07/2016
ms.prod	sql
ms.prod_service	database-engine, sql-database, sql-data-warehouse, pdw
ms.reviewer
ms.technology	t-sql
ms.topic	language-reference
dev_langs	TSQL
helpviewer_keywords	concatenate strings string concatenation += (concatenate operator)
ms.assetid	4aaeaab7-9b2b-48e0-8487-04ed672ebcb1
author	rothja
ms.author	jroth
monikerRange	>=aps-pdw-2016||=azuresqldb-current||=azure-sqldw-latest||>=sql-server-2016||=sqlallproducts-allversions||>=sql-server-linux-2017||=azuresqldb-mi-current

+= (String Concatenation Assignment) (Transact-SQL)

[!INCLUDEtsql-appliesto-ss2008-all_md]

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;  

[!INCLUDEssResult]

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

[!INCLUDEssResult]

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)