Update the id of the second row based on the first id

Question

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 ;

Answer 1

Join the table to a query that returns the minimum value sid for each id and returns itself again to get the value with that minimum sid## Rows of #:

UPDATE tablename t1
INNER JOIN (
  SELECT MIN(sid) sid, id
  FROM tablename
  GROUP BY id
) t2 ON t2.id = t1.id AND t2.sid 
View
Demo. 

For MySql 8.0, if you use the 
ROW_NUMBER() window function, you only need 1 connection to complete: 
UPDATE tablename t1
INNER JOIN (
  SELECT *, ROW_NUMBER() OVER (PARTITION BY id ORDER BY sid) rn
  FROM tablename
) t2 ON t2.id = t1.id  
SET t1.amount = t2.amount
WHERE t2.rn = 1;
View
Demo.