Mysql transactions within transactions

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

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.