sql find duplicate entry and insert into new column

Question

I have a table with columns: Date, Phone, Name, and Event

I need a query that will first recognize the duplicate phone entry, and then assign the name of whichever one has the earlier date to the event column.

Answer 1

Use:

UPDATE x
   SET x.event = y.name
  FROM YOUR_TABLE x
  JOIN YOUR_TABLE y ON y.phone = x.phone
  JOIN (SELECT t.phone,
               MIN(t.date) As min_date
          FROM YOUR_TABLE t
      GROUP BY t.phone
        HAVING COUNT(*) > 1) z ON z.phone = y.phone
                              AND z.min_date = y.date
                              AND z.min_date < x.date

But it doesn't address if there are duplicates of the minimum value.