title: Delete (make null) duplicate field values
body: <p>i've searched for a solution for this but haven't found a complete one. I have dozens of tables that each contain thousands of line features.  whenever a line feature is split another record is created but the new line (record) still has the old ASSETID. This means a duplicate ASSETID is born.  Is maintenance python script that can find all the duplicate ASSETID's and make them null?  this would leave just the original ASSETID, i have a script that would be run afterwards that would populate the ASSETID field with a new, randomly generated ASSETID. i've been able to create lists all the duplicate values, a list of how many times a value occurs, a new column on the table that has a 'Y' if value is repeated, etc. but have yet been able to remove duplicate field values while retaining everything else in the row.</p>