geoff5 (4/23/2013)
After reading through the thread, I see that none of the solutions offered thus far have recognized the necessity of treating the rows with a known IDNo differently than the rows with a null IDNo.
Not quite true.
In my script you can see that all the "duplicate candidates" (T2) must have IDNo IS NULL.
There no condition on T1.IDNo, as "primary" entry may have it NULL as well, according to the OP description.
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Code for TallyGenerator