The expression parameter requires an aggregate function. For example, the following is a legal expression:

Count(Quantity)

But this expression is not:

Sum (Quantity * UnitPrice)

If you must perform an operation on two or more columns, you should create a DataColumn, set its Expression property to an appropriate expression, and use an aggregate expression on the resulting column. In that case, given a DataColumn with the name "total", and the Expression property set to this:

"Quantity * UnitPrice"

The expression argument for the Compute method would then be this:

Sum(total)

The second parameter, filter, determines which rows are used in the expression. For example, if the table contains a date column named "colDate", you could limit the rows with the following expression:

colDate > 1/1/99 AND colDate < 17/1/99

For rules on creating expressions for both parameters, see the DataColumn..::.Expression property.

The following example sums the values of a column named "Total", for the salesperson whose identification number is five.

Private Sub ComputeBySalesSalesID(ByVal dataSet As DataSet)
    ' Presumes a DataTable named "Orders" that has a column named "Total."
    Dim table As DataTable
    table = dataSet.Tables("Orders")

    ' Declare an object variable.
    Dim sumObject As Object
    sumObject = table.Compute("Sum(Total)", "EmpID = 5")
 End Sub

private void ComputeBySalesSalesID(DataSet dataSet)
{
    // Presumes a DataTable named "Orders" that has a column named "Total."
    DataTable table;
    table = dataSet.Tables["Orders"];

    // Declare an object variable.
    object sumObject;
    sumObject = table.Compute("Sum(Total)", "EmpID = 5");
}

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

.NET Framework

.NET Compact Framework

XNA Framework

Reference

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