STRING_AGG (Transact-SQL)

THIS TOPIC APPLIES TO:yesSQL Server (starting with 2017)yesAzure SQL DatabasenoAzure SQL Data Warehouse noParallel Data Warehouse

Concatenates the values of string expressions and places separator values between them. The separator is not added at the end of string.

Topic link icon Transact-SQL Syntax Conventions

Syntax

STRING_AGG ( expression, separator [ <order_clause> ] )

<order_clause> ::=   
    WITHIN GROUP ( ORDER BY <order_by_expression_list> [ ASC | DESC ] )   

Arguments

separator
Is an expression of NVARCHAR or VARCHAR type that is used as separator for concatenated strings. It can be literal or variable.

expression
Is an expression of any type. Expressions are converted to NVARCHAR or VARCHAR types during concatenation. Non-string types are converted to NVARCHAR type.


Optionally specify order of concatenated results using WITHIN GROUP clause:

WITHIN GROUP ( ORDER BY <order_by_expression_list> [ ASC | DESC ] )

A list of non-constant expressions that can be used for sorting results. Only one order_by_expression is allowed per query. The default sort order is ascending.

Return Types

Return type is depends on first argument (expression). If input argument is string type (NVARCHAR, VARCHAR), result type will be same as input type. The following table lists automatic conversions:

Input expression type Result
NVARCHAR(MAX) NVARCHAR(MAX)
VARCHAR(MAX) VARCHAR(MAX)
NVARCHAR(1…4000) NVARCHAR(4000)
VARCHAR(1…8000) VARCHAR(8000)
int, bigint, smallint, tinyint, numeric, float, real, bit, decimal, smallmoney, money, datetime, datetime2, NVARCHAR(4000)

Remarks

STRING_AGG aggregate takes all expressions from rows and concatenates them into a single string. Expression values are implicitly converted to string types and then concatenated. The implicit conversion to strings follows the existing rules for data type conversions. For more information about data type conversions, see CAST and CONVERT (Transact-SQL).

If the input expression is type VARCHAR, the separator cannot be type NVARCHAR.

Null values are ignored and the corresponding separator is not added. To return a place holder for null values, use the ISNULL function as demonstrated in example B.

STRING_AGG is available in any compatibility level.

Examples

A. Generate list of names separated in new lines

The following example produces a list of names in a single result cell, separated with carriage returns.

SELECT STRING_AGG (FirstName, CHAR(13)) AS csv 
FROM Person.Person; 

Here is the result set.

csv
Syed
Catherine
Kim
Kim
Kim
Hazem
...

NULL values found in name cells are not returned in result.

Note

If using the Management Studio Query Editor, the Results to Grid option cannot implement the carriage return. Switch to Results to Text to see the result set properly.

B. Generate list of names separated with comma without NULL values

The following example replaces null values with 'N/A' and returns the names separated by commas in a single result cell.

SELECT STRING_AGG ( ISNULL(FirstName,'N/A'), ',') AS csv 
FROM Person.Person; 

Here is the result set.

Csv
John,N/A,Mike,Peter,N/A,N/A,Alice,Bob

C. Generate comma-separated values

SELECT 
STRING_AGG(CONCAT(FirstName, ' ', LastName, ' (', ModifiedDate, ')'), CHAR(13)) 
  AS names 
FROM Person.Person; 

Here is the result set.

names
Ken Sánchez (Feb 8 2003 12:00AM)
Terri Duffy (Feb 24 2002 12:00AM)
Roberto Tamburello (Dec 5 2001 12:00AM)
Rob Walters (Dec 29 2001 12:00AM)
...
Note

If using the Management Studio Query Editor, the Results to Grid option cannot implement the carriage return. Switch to Results to Text to see the result set properly.

Article and their tags are separated into different tables. Developer wants to return one row per each article with all associated tags. Using following query:

SELECT a.articleId, title, STRING_AGG (tag, ',') as tags 
FROM dbo.Article AS a       
LEFT JOIN dbo.ArticleTag AS t 
    ON a.ArticleId = t.ArticleId 
GROUP BY a.articleId, title;

Here is the result set.

articleId title tags
172 Polls indicate close election results politics,polls,city council
176 New highway expected to reduce congestion NULL
177 Dogs continue to be more popular than cats polls,animals

E. Generate list of emails per towns

The following query finds the email addresses of employees and groups them by towns:

SELECT town, STRING_AGG (email, ';') AS emails 
FROM dbo.Employee 
GROUP BY town; 

Here is the result set.

town emails
Seattle syed0@adventure-works.com;catherine0@adventure-works.com;kim2@adventure-works.com
LA sam1@adventure-works.com;hazem0@adventure-works.com

Emails returned in the emails column can be directly used to send emails to group of people working in some particular towns.

F. Generate a sorted list of emails per towns

Similar to previous example, the following query finds the email addresses of employees, groups them by town, and sorts the emails alphabetically:

SELECT town, 
    STRING_AGG (email, ';') WITHIN GROUP (ORDER BY email ASC) AS emails 
FROM dbo.Employee 
GROUP BY town; 

Here is the result set.

town emails
Seattle catherine0@adventure-works.com;kim2@adventure-works.com;syed0@adventure-works.com
LA hazem0@adventure-works.com;sam1@adventure-works.com

See Also

String Functions (Transact-SQL)