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Use FOR JSON output in SQL Server and in client apps

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Applies to: SQL Server 2016 (13.x) and later Azure SQL Database Azure SQL Managed Instance Azure Synapse Analytics (serverless SQL pool only)

The following examples demonstrate some of the ways to use the FOR JSON clause and its JSON output in SQL Server or in client apps. Format query results as JSON with FOR JSON

In Fabric Data Warehouse, FOR JSON must be the last operator in the query, and so is not allowed inside subqueries, as in the examples in this article.

Use FOR JSON output in SQL Server variables

The output of the FOR JSON clause is of type nvarchar(max), so you can assign it to any variable, as shown in the following example.

DECLARE @x NVARCHAR(MAX) =
  (SELECT TOP 10 *
     FROM Sales.SalesOrderHeader
     FOR JSON AUTO)

Use FOR JSON output in SQL Server user-defined functions

You can create user-defined functions that format result sets as JSON and return this JSON output. The following example creates a user-defined function that fetches some sales order detail rows and formats them as a JSON array.

CREATE FUNCTION GetSalesOrderDetails(@salesOrderId int)  
 RETURNS NVARCHAR(MAX)  
AS  
BEGIN  
   RETURN (SELECT UnitPrice, OrderQty  
           FROM Sales.SalesOrderDetail  
           WHERE SalesOrderID = @salesOrderId  
           FOR JSON AUTO)  
END

You can use this function in a batch or query, as shown in the following example.

DECLARE @x NVARCHAR(MAX) = dbo.GetSalesOrderDetails(43659)

PRINT dbo.GetSalesOrderDetails(43659)

SELECT TOP 10
  H.*, dbo.GetSalesOrderDetails(H.SalesOrderId) AS Details
FROM Sales.SalesOrderHeader H

Merge parent and child data into a single table

In the following example, each set of child rows is formatted as a JSON array. The JSON array becomes the value of the Details column in the parent table.

SELECT TOP 10 SalesOrderId, OrderDate,  
      (SELECT TOP 3 UnitPrice, OrderQty  
         FROM Sales.SalesOrderDetail D  
         WHERE H.SalesOrderId = D.SalesOrderID  
         FOR JSON AUTO) AS Details  
INTO SalesOrder  
FROM Sales.SalesOrderHeader H

Update the data in JSON columns

The following example demonstrates that you can update the value of a column that contains JSON text.

UPDATE SalesOrder  
SET Details =  
     (SELECT TOP 1 UnitPrice, OrderQty  
       FROM Sales.SalesOrderDetail D  
       WHERE D.SalesOrderId = SalesOrder.SalesOrderId  
      FOR JSON AUTO)

Use FOR JSON output in a C# client app

The following example shows how to retrieve the JSON output of a query into a StringBuilder object in a C# client app. Assume that the variable queryWithForJson contains the text of a SELECT statement with a FOR JSON clause.

var queryWithForJson = "SELECT ... FOR JSON";
using(var conn = new SqlConnection("<connection string>"))
{
    using(var cmd = new SqlCommand(queryWithForJson, conn))
    {
        conn.Open();
        var jsonResult = new StringBuilder();
        var reader = cmd.ExecuteReader();
        if (!reader.HasRows)
        {
            jsonResult.Append("[]");
        }
        else
        {
            while (reader.Read())
            {
                jsonResult.Append(reader.GetValue(0).ToString());
            }
        }
    }
}

Learn more about JSON in the SQL Database Engine

Microsoft videos

For a visual introduction to the built-in JSON support in SQL Server and Azure SQL Database, see the following videos:

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