Combine Multiple Rows into One String in SQL Server | STRING_AGG Explained
This lesson covers how to use the T-SQL STRING_AGG function to concatenate (combine) values from multiple rows into a single string.
What is STRING_AGG?
STRING_AGG is an aggregate function (like SUM or AVG) that concatenates string values from multiple rows into a single string. It takes two required parameters:
Basic syntax:
STRING_AGG (expression, separator)
Where:
expression: The value to concatenate (usually a column)
separator: The string to insert between each value
Full query examples:
Basic concatenation:
SELECT
CategoryID,
STRING_AGG(ProductName, '; ') AS Products
FROM Products
GROUP BY CategoryID;
With sorting:
SELECT
CategoryID,
STRING_AGG(ProductName, '; ')
WITHIN GROUP (ORDER BY ProductName) AS Products
FROM Products
GROUP BY CategoryID;
Important notes:
STRING_AGG ignores NULL values automatically
The function was introduced in SQL Server 2017
It's also available in Azure SQL Database
The result type is NVARCHAR or VARCHAR depending on input
Common use cases:
Creating comma-separated lists for reports
Building email recipient lists
Generating JSON-like strings
Formatting output for export files
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