Stopping a custom SQLCLR aggregate early - sql-server

Question

Let's say I want I have a table with the following columns and values:
| BucketID | Value |
|:-----------|------------:|
| 1 | 3 |
| 1 | 2 |
| 1 | 1 |
| 2 | 0 |
| 2 | 1 |
| 2 | 5 |
Let's pretend I want to partition over BucketId and Multiply the values in the partition:
SELECT DISTINCT BucketId, MULT(Value) OVER (PARTITION BY BucketId)
Now, there is no built-in Aggregate MULT function so I am writing my own using SQL CLR:
using System;
using System.Data.SqlTypes;
using Microsoft.SqlServer.Server;
[Serializable]
[SqlUserDefinedAggregate(Format.Native, Name = "MULT")]
public struct MULT
{
private int runningSum;
public void Init()
{
runningSum = 1;
}
public void Accumulate(SqlInt32 value)
{
runnningSum *= (int)value;
}
public void Merge(OverallStatus other)
{
runnningSum *= other.runningSum;
}
public SqlInt32 Terminate()
{
return new SqlInt32(runningSum);
}
}
What my question boils down to is, let's assume I hit a 0 in Accumulate or Merge, there is no point continuing on. If that is the case, how can I return 0 as soon as I hit 0?

Answer 1

You cannot force a termination since there is no way to control the workflow. SQL Server will call the Terminate() method as each group finishes processing its set.
However, since the state of the UDA is maintained across each row processed in a group, you can simply check runningSum to see if it's already 0 and if so, skip any computations. This would save some slight amount of time processing.
In the Accumulate() method, the first step will be to check if runningSum is 0, and if true, simply return;. You should also check to see if value is NULL (something you are not currently checking for). After that, check the incoming value to see if it is 0 and if true, then set runningSum to 0 and return;.
public void Accumulate(SqlInt32 value)
{
if (runningSum == 0 || value.IsNull)
{
return;
}
if (value.Value == 0)
{
runningSum = 0;
return;
}
runningSum *= value.Value;
}
Note: Do not cast value to int. All Sql* types have a Value property that returns the expected native .NET type.
Finally, in the Merge method, check runnningSum to see if it is 0 and f true, simply return;. Then check other.runningSum to see if it is 0, and if true, then set runnningSum to 0.