STRING_AGG (Transact-SQL)

• 04/19/2017
• 3 minutes to read
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APPLIES TO: SQL Server Azure SQL Database Azure SQL Data Warehouse Parallel Data Warehouse

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

Transact-SQL Syntax Conventions

Syntax

STRING_AGG ( expression, separator ) [ <order_clause> ]

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

Arguments

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.

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

<order_clause>
Optionally specify order of concatenated results using WITHIN GROUP clause:

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

<order_by_expression_list>

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:

Remarks

STRING_AGG is an aggregate function that 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.

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

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.

C. Generate comma-separated values

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

Here is the result set.

D. Return news articles with related tags

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.

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.

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.

See also

CONCAT (Transact-SQL)
CONCAT_WS (Transact-SQL)
FORMATMESSAGE (Transact-SQL)
QUOTENAME (Transact-SQL)
REPLACE (Transact-SQL)
REVERSE (Transact-SQL)
STRING_ESCAPE (Transact-SQL)
STUFF (Transact-SQL)
TRANSLATE (Transact-SQL)
Aggregate Functions (Transact-SQL)
String Functions (Transact-SQL)