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DataTable.Compute Method

.NET Framework 3.5

Other Versions

Computes the given expression on the current rows that pass the filter criteria.

Namespace: System.Data
Assembly: System.Data (in System.Data.dll)

Syntax

C++

JScript

public Object Compute(
	string expression,
	string filter
)

Parameters

expression: Type: System.String
The expression to compute.

filter: Type: System.String
The filter to limit the rows that evaluate in the expression.

Return Value

Type: System.Object
An Object, set to the result of the computation. If the expression evaluates to null, the return value will be Value.

Remarks

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.

Examples

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

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");
}

Platforms

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

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Version Information