C# 4 and .NET 4

966 ❘ ChaPTer 34 .net prOGrAmminG with sQl server
In the code sample, the variable sum is used for accumulation of all values of a group. In the Init() method,
the variable sum is initialized for every new group to accumulate. The method Accumulate() , which is
invoked for every value, adds the value of the parameter to the sum variable. With the Merge() method,
one aggregated group is added to the current group. Finally, the method Terminate() returns the result of
a group:
[Serializable]
[SqlUserDefinedAggregate(Format.Native)]
public struct SampleSum
{
private int sum;
public void Init()
{
sum = 0;
}
public void Accumulate(SqlInt32 Value)
{
sum += Value.Value;
}
public void Merge(SampleSum Group)
{
sum += Group.sum;
}
}
public SqlInt32 Terminate()
{
return new SqlInt32(sum);
}
code snippet SqlSamplesUsingAdventureWorks/SampleSum.cs
You can use the Aggregate template from Visual Studio to create the core code for
building the user - defi ned aggregate. The template from Visual Studio creates a struct
that uses the SqlString type as a parameter and return type with the Accumulate and
Terminate methods. You can change the type to a type that represents the requirement
of your aggregate. In the example, the SqlInt32 type is used.
using user - defined aggregates
The user - defi ned aggregate can be deployed either with Visual Studio or with the CREATE AGGREGATE
statement. Following the CREATE AGGREGATE is the name of the aggregate, the parameter (@value int) ,
and the return type. EXTERNAL NAME requires the name of the assembly and the .NET type including the
namespace:
CREATE AGGREGATE [SampleSum] (@value int) RETURNS [int] EXTERNAL NAME
[Demo].[SampleSum]
After the user - defi ned aggregate has been installed, it can be used as shown in the following
SELECT statement, where the number of ordered products is returned by joining the Product
and PurchaseOrderDetail tables. For the user - defi ned aggregate, the OrderQty column of the
Order PurchaseOrderDetail table is defi ned as an argument:
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