Question

In a PHP script working with a mysql database, I recently had the need to use a transaction at a point that happened to be inside another transaction. All my tests seem to indicate this is working out fine, but I can’t find any documentation on this usage.

I want to be sure – are transactions within transactions valid in mysql? If so, is there a way to find out how many levels deep you are in nested transactions? (ie. how many rollbacks it would take to return to normal)

Thanks in advance,
Brian

Answer 1

This page of the manual might interest you : 12.3.3. Statements That Cause an Implicit Commit; quoting a few sentences :

The statements listed in this section
(and any synonyms for them) implicitly
end a transaction, as if you had done
a COMMIT before executing the
statement.

And, a bit farther in the page :

Transaction-control and locking
statements. BEGIN, LOCK TABLES,
SET autocommit = 1 (if the value is
not already 1), START TRANSACTION,
UNLOCK TABLES.

See also this paragraph :

Transactions cannot be nested.
This is
a consequence of the implicit commit
performed for any current transaction
when you issue a START TRANSACTION
statement or one of its synonyms.