PHP/mysqli: unintended rollback in query across two mysql databases

Question

I am trying to restore some data from a backup database. All tables are Innodb, I am using PHP/mysqli for scripting. I am trying with or without a transaction, but that makes no difference.

So I open a DB connection as user "root" and do:

INSERT INTO maindb.table1 SELECT * FROM backupdb.table1 WHERE user_id = 1234;

Afterwards, affected_rows returns 825 rows, as it should be. There does not appear to be an error anywhere. An immediate

SELECT COUNT(*) FROM table1 WHERE user_id = 1234

shows 825 rows.

However, upon the script exiting, the row count in table1 for user_id 1234 is again 0.

It appears that there is an automatic rollback at the end, but I cannot for the life of me understand why. Maybe it is because there are two databases involved? I have never heard of such a behavior before.

When I run the same query on the mysql command line as root, the rows are properly inserted, and the row count afterwards is 825.

Here is my example code:

$db = new mysqli(
    'localhost',
    'root',
    $password,
    'maindb'
);

$uid = 1234;

//$db->begin_transaction();
$db->query("INSERT INTO maindb.table1 SELECT * FROM backupdb.table1 WHERE user_id = $uid");
echo "table1: " . $db->affected_rows . "\n";
$st = $db->query("SELECT count(*) FROM maindb.table1 WHERE user_id = $uid");
var_dump($st->fetch_all());
//$db->commit();

$db->close();

Result:

table1: 825
array(1) {
  [0]=>
  array(1) {
    [0]=>
    string(3) "825"
  }
}

Any ideas why the rollback is happening and how to avoid it?

Answer 1

Oops. Found it, here is the culprit:

REPLACE INTO maindb.user SELECT * FROM backupdb.user WHERE id =  $uid

This was at the end of the script, I had omitted that. What mysql REPLACE does is delete the user (including all dependent data in other tables -> ON DELETE CASCADE) and insert the row anew. That means that all of the data previously copied is deleted. Sorry for the confusion.