Hope this satisfies your need:

I created a new class (called Test.Common.Utility) to do this.  It performs a simple SQL select on a %Persistent table to find a specific value in a column.  The code is as follows:

Include EnsHL7
Class Test.Common.Utility Extends Ens.Rule.FunctionSet
{
ClassMethod CheckTable(pCSN As %String) As %Boolean
{
    Set output = $$$NO
    
    &SQL(Declare C11 Cursor for select CSN into :tCSN from Test_Record.SampleTable where (CSN = :pCSN))
    &SQL(Open C11)
    &SQL(Fetch C11)
    if SQLCODE = 0 { Set output = $$$YES }
    &SQL(Close C11)

    Quit output
}
}

My rule to implement this function looks like: