Can you please elaborate on this? I'm unfamiliar with these platforms. Is that kind of column always returned in a result set?

Yes. It's appended to the inner query for counting rows and used by the outer query for filtering.

For instance, on DB2:

$conn = DriverManager::getConnection([
    'driver'   => 'ibm_db2',
    'user'     => 'db2inst1',
    'password' => 'Passw0rd',
    'dbname'   => 'doctrine',
]);

$sql = $conn->getDatabasePlatform()
    ->modifyLimitQuery('SELECT TEST_INT, TEST_STRING from FETCH_TABLE', 1, 1);

echo $sql, PHP_EOL; // formatted for readability
/*
SELECT db22.*
FROM (
    SELECT db21.*, ROW_NUMBER() OVER () AS DC_ROWNUM
    FROM (
        SELECT TEST_INT, TEST_STRING from FETCH_TABLE
    ) db21
) db22
WHERE db22.DC_ROWNUM >= 2
  AND db22.DC_ROWNUM <= 2
*/

$data = $conn->fetchAllAssociative($sql);
var_dump($data);
/*
array(1) {
  [0] =>
  array(3) {
    'TEST_INT' =>
    int(2)
    'TEST_STRING' =>
    string(3) "foo"
    'DC_ROWNUM' =>
    string(1) "2"
  }
}
*/

Despite the fact that we selected two columns, the result contains three.

UPD: I added a test for it.

I see, the DBAL does that here:

Thanks for the explanation, this looks good.

Good point about adding a test also, I think you discovered a bug 😅

I think you discovered a bug 😅

Yeah, 4½ years ago (#2374) 😅

@tswcode does it look like what you're looking for?

Indeed, that looks promising. I will test it as soon as I am back at work (on monday). :)

I'm not sure about missing tests for the catched exceptions for rowCount() and columnCount(). There might be value that a DriverException is only internally handled and that the methods are converting them to the expected exceptions.

The tests are missing because there's no clear understanding of how these methods could throw an exception in any of the existing drivers. Not that it's impossible, they just were never added.

The general concept is that the driver-level methods may throw driver exceptions while the wrapper should convert them into a generic or specialized wrapper-level exception (e.g. ConnectionLost). The only reason I'm making this change now is that the new fetch mode calls columnCount() that doesn't handle the documented driver exception. But a method in the wrapper layer cannot throw a driver exception, so it must be handled. The only right place to handle the exception from the driver columnCount() is in the wrapper columnCount().

There's absolutely a lot of work on exception handling (#4160 is just the beginning).

Unfortunately I was busy this week, I just noticed that this feature has been added to the branch 3.0.x.

@morozov Could you also add it to the branch 2.11.x ?

@tswcode see #4338.