My original data is as follows:

sid id  amount
1   12  30
2   45  30
3   45  50
4   78  80
5   78  70

The desired output is as follows:

sid id  amount
1   12  30
2   45  30
3   45  30
4   78  80
5   78  80

The purpose is to get the amount of the first occurrence of id and update the amount when it appears the second time I'm trying the following code:

UPDATE foo AS f1
  JOIN
  ( SELECT cur.sl, cur.id,
           cur.amount AS balance 
    FROM foo AS cur
      JOIN foo AS prev
        ON prev.id = cur.id
    GROUP BY cur.tstamp
  ) AS p
  ON p.id = a.id
SET a.amount = p.amount ;