If AutoCommit is on, begin_work() will turn it off, until the transaction gets commited or rolled back, so this code works:

use DBI;

use strict;
use warnings;

my $dsn = "DBI:mysql:database=test;host=blah";
my $dbh = DBI->connect($dsn, 'root', 'abcd', {RaiseError => 1, AutoCom
+mit => 1});
my $command = "update test set a = a + 1";
my $sth = $dbh->prepare($command);
$dbh->begin_work();
$sth->execute();
$sth->execute();
$sth->execute();
$sth->execute();
$dbh->commit();
[download]

If AutoCommit is off, then you are sort of in an implicit transaction already, and when you call begin_work is issues an error. I personally don't like this behavior, but this is how it works. If you run this code (the only difference is that AutoCommit is off:

use DBI;

use strict;
use warnings;

my $dsn = "DBI:mysql:database=test;host=blah";
my $dbh = DBI->connect($dsn, 'root', 'abcd', {RaiseError => 1, AutoCom
+mit => 0});
my $command = "update test set a = a + 1";
my $sth = $dbh->prepare($command);
$dbh->begin_work();
$sth->execute();
$sth->execute();
$sth->execute();
$sth->execute();
$dbh->commit();
[download]

You get this error:

DBD::mysql::db begin_work failed: Already in a transaction at math1.pl
+ line 10.
DBD::mysql::db begin_work failed: Already in a transaction at math1.pl
+ line 10.
[download]

Summary: the logic behind is, regardless whether I like it: If AutoCommit is on, and you want a transaction, obviously I have to turn it off for you as long as you remain in the transaction, so that you can decide the poitn to commit or rollback; But if AutoCommit is off, you are already in sort of transaction, why you start a transaction in a transaction?