MySQL transaction with accounting application

Question

I have a table like the following:

transaction_id
user_id
other_user_id
trans_type
amount

This table is used to maintain the account transa

Answer 1

The problem is that the concept of the "user account" is "scattered" through many rows in your table. With the current representation, I think you can't "lock the user account" (so to speak), so you are open to race conditions when modifying them.

A possible solution would be to have another table with user accounts, and lock a row in that table , so anybody needing to modify the account can try to obtain the lock, do the operation, and release the lock.

For instance:

begin transaction;
update db.accounts set lock=1 where account_id='Bob' and lock=0;
if (update is NOT successful) # lock wasn't on zero
  {
  rollback;
  return;
  }
if (Bob hasn't enough funds)
  {
  rollback;
  return;
  }

insert into db.transactions value (?, 'Bob', 'Alice', 'Sent', -3000);
insert into db.transactions value (?, 'Alice', 'Bob', 'Received',  3000);
update db.accounts set lock=0 where account_id='Bob' and lock=1;

commit;

... or something like that.