Description:
------------
Calling MySQL's PDO::exec() with an update query that doesn't change existing data on an existing row always returns 0. With PostgreSQL, always returns 1. If, in MySQL, a trigger is added to the updating table, the trigger is executed (and inserts may occur) but the result is still 0.
I am aware of the differences between Postgresql and Mysql regarding updates due to MVCC, but if a trigger changes something, it should return the number of affected rows.

Test script:
---------------
/* Assuming the following sql structure:

create table test(
 id int(11) not null,
 name varchar(128) not null
);
insert into test values(1, 'test_name');
*/
$query = "update test set name='xpto' where id=1";
echo $pdo->exec($query); // first run returns 1, all others 0

/* Add the following trigger:
create table control(
 counter int(11) not null
);
insert into control values(0);

CREATE TRIGGER test_update     
 BEFORE UPDATE ON test    
 FOR EACH ROW BEGIN 
 UPDATE control set counter=counter+1;
 END$$
*/
$query = "update test set name='xpto' where id=1";
echo $pdo->exec($query); // first run returns 1, all others 0, but control table is updated