MySQL update table with values from same table

join, mysql

Solution

think this going to work:

Try 1

UPDATE score_list AS t2
LEFT JOIN score_list AS t1 ON
  (t1.id = t2.id AND t1.flag = t2.flag AND t1.gameId = 1)
SET
  t1.score = t1.score + t2.score,
  t2.gameId = IF(t1.gameId IS NULL, 1, t2.gameId)
WHERE t2.gameId = 2;

DELETE FROM score_list WHERE gameId = 2;

Try 2

# add scores to gameId = 1
UPDATE score_list AS t2
LEFT JOIN score_list AS t1 ON
  (t1.id = t2.id AND t1.flag = t2.flag AND t1.gameId = 1)
SET
  t1.score = t1.score + t2.score
WHERE t2.gameId = 2;

# try to move gameID 2 to gameId 1, using ignore to allow rows to fail, as gameId alredy exists
UPDATE IGNORE score_list SET gameId = 1 WHERE gameId = 2;

# delete all not updated rows from last query
DELETE FROM score_list WHERE gameId = 2;

Problem

I have a 4 column table, the primary key is a composite of id, gameId and flag. ``` id | gameId | score | flag -------------------------- 1 | 1 | 10 | 1 1 | 1 | 20 | 0 2 | 1 | 1 | 0 1 | 2 | 10 | 1 3 | 2 | 1 | 0 ``` I need to update the table so that: All of gameId 2 scores are added to gameId 1 where the id and flag is the same. (e.g. row 1 would have a score of 20 by adding the scores of row 1 and row 4) If the above happens the gameId 2 row needs to be deleted. Where the above isn't found (e.g. there is a row where the gameId is 2 but the id and flag don't match another row), the gameId can just be changed to 1. So my table after the SQL is complete should look like this: ``` id | gameId | score | flag -------------------------- 1 | 1 | 20 | 1 1 | 1 | 20 | 0 2 | 1 | 1 | 0 3 | 1 | 1 | 0 ``` How can I write this in SQL? Thanks :)

Original source