• Article

Specifying the Data Source by Using the FROM Clause

Use the FROM clause to pull data from one or more tables or views into the table you want to update. The following example modifies the SalesYTD column in the SalesPerson table to reflect the most recent sales recorded in the SalesOrderHeader table.

USE AdventureWorks2008R2;
GO
UPDATE Sales.SalesPerson
SET SalesYTD = SalesYTD + SubTotal
FROM Sales.SalesPerson AS sp
JOIN Sales.SalesOrderHeader AS so
    ON sp.BusinessEntityID = so.SalesPersonID
    AND so.OrderDate = (SELECT MAX(OrderDate)
                        FROM Sales.SalesOrderHeader
                        WHERE SalesPersonID = sp.BusinessEntityID);
GO

The previous example assumes that only one sale is recorded for a specified salesperson on a specific date and that updates are current. If more than one sale for a specified salesperson can be recorded on the same day, the example shown does not work correctly. The example runs without error, but each SalesYTD value is updated with only one sale, regardless of how many sales actually occurred on that day. This is because a single UPDATE statement never updates the same row two times.

In the situation in which more than one sale for a specified salesperson can occur on the same day, all the sales for each sales person must be aggregated together within the UPDATE statement, as shown in the following example.

USE AdventureWorks2008R2;
GO
UPDATE Sales.SalesPerson
SET SalesYTD = SalesYTD + 
    (SELECT SUM(so.SubTotal) 
     FROM Sales.SalesOrderHeader AS so
     WHERE so.OrderDate = (SELECT MAX(OrderDate)
                           FROM Sales.SalesOrderHeader AS so2
                           WHERE so2.SalesPersonID = so.SalesPersonID)
     AND Sales.SalesPerson.BusinessEntityID = so.SalesPersonID
     GROUP BY so.SalesPersonID);
GO