MySQL: Add sequence column based on another field

Question

I\'m working on some legacy code/database, and need to add a field to the database which will record a sequence number related to that (foreign) id.

Example table da

Answer 1

This should work but is probably slow:

CREATE temporary table seq ( id int, seq int);
INSERT INTO seq ( id, seq )
    SELECT id, 
      (SELECT count(*) + 1 FROM test c 
      WHERE c.id < test.id AND c.account = test.account) as seq 
    FROM test;

UPDATE test INNER join seq ON test.id = seq.id SET test.seq = seq.seq;

I have called the table 'test'; obviously that needs to be set correctly. You have to use a temporary table because MySQL will not let you use a subselect from the same table you are updating.