John,
Just curious... Why do your messages always have the > marks < around them? That's not the usual when entering a new UT message.
>> I'm trying to update of replace a field in a table, using <
>> another table.
You already have a good suggestion from someone else about how to do this, but why is it necessary? If the policies' group_code is supposed to always be the same as the client's, just keep the code in the client table and get rid of it in the policy table. When you need to know the group_code for a policy, get it with a join to the client table in your SQL SELECT statement.
Unless there is some reason that a policy's code could be different from the current client code, you are denormalizing your table design which results in this kind of maintenance headache.