Mysql transaction rollback on failure in update

Question

With a simple transaction as

START TRANSACTION;
UPDATE posts SET status='approved' where post_id='id' AND status != 'approved';
.. other queries ...
COMMIT;

I want to perform the transaction only once when changing the status; but the above UPDATE will not give an error to rollback the transaction when no row is updated.

How can I limit the transaction to commit only if the row is updated (I mean the status is changed).

Solution 1

Here is in PHP (haven't tested, needs adapting to your situation):

mysql_query('START TRANSACTION;')
mysql_query("UPDATE posts SET status='approved' where post_id='id' AND status != 'approved';");
if (mysql_affected_rows()){
    mysql_query('COMMIT');
} else {
    mysql_query('ROLLBACK');
}

Or, If you want to be clever and do it in SQL (using ROW_COUNT() and IF):

START TRANSACTION;
UPDATE posts SET status='approved' where post_id='id' AND status != 'approved';
SELECT ROW_COUNT() INTO @affected_rows;
-- .. other queries ...
IF (affected_rows > 0) THEN
    COMMIT;
ELSE
    ROLLBACK;
END IF

Solution 2

You will need to do this in some sort of programming logic - maybe a stored procedure is best.

• START TRANSACTION
• run UPDATE query
• SELECT ROW_COUNT() INTO some_variable
• IF (some_variable>0) THEN [run the other statements including COMMIT] ELSE ROLLBACK

Comments

[Googlebot]

Perfect! As a matter of fact, I am in PHP :)

[Vyktor]

@Ali I recommend updating tags than :P

[MatBailie]

Don't run "the other queries" then roll them back, that's a bit inneficient. Just move them into the same code block as the COMMIT, so they only ever execute if needed (as opposed to always executing, then rolling them back sometimes).

[Googlebot]

@Dems very good point; I always try to avoid ROLLBACK and execute COMMIT if possible.

[Vyktor]

@Dems I assumed that he may have more queries which will affect records and which will matter... So the real condition would be: (affected_1 + affected_2 + .... > 0) THEN but in the case that this is the only relevant one, than you're of course right.