PHP：PDO rowCount（）有时返回0？ [重复]

I am using the fantastic last_insert_id trick described here, but now run into the problem of non-deterministic behavior.

The PHP code works approximately every other time I run it. This is on a completely idle system (no production running simultaneously).

Is there anything I am forgetting here? What could the problem be?

My PHP code:

$query = "UPDATE `session` 
                SET `date_access` = NOW(), someField = LAST_INSERT_ID(someField) 
                WHERE ID = :cookie LIMIT 1 ;";
    $stmt = $dbh->prepare($query);
    $stmt->bindParam(':cookie', $_COOKIE['x']);
    if ($stmt->execute()) {
        $count = $stmt->rowCount();
        if ($count == 1) {
            $result = $dbh->lastInsertId();
        } 
    }

The code is run with an existing "cookie" value every time, but the $count is 0 (instead of 1) every other time the code runs.

And this is the table:

            SET NAMES utf8;
            SET time_zone = '+00:00';
            SET foreign_key_checks = 0;
            SET sql_mode = 'NO_AUTO_VALUE_ON_ZERO';

            SET NAMES utf8mb4;

            DROP TABLE IF EXISTS `session`;
            CREATE TABLE `session` (
              `ID` char(50) CHARACTER SET ascii COLLATE ascii_bin NOT NULL,
              `date_create` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP,
              `date_access` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
              `someField` bigint(20) unsigned NOT NULL,
              UNIQUE KEY `ID` (`ID`),
              KEY `someField` (`someField`),
              CONSTRAINT `session_ibfk_2` FOREIGN KEY (`someTable`) REFERENCES `someTable` (`ID`) ON DELETE CASCADE ON UPDATE CASCADE
            ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

</div>

https://dev.mysql.com/doc/refman/5.7/en/mysql-affected-rows.html says:

For UPDATE statements, the affected-rows value by default is the number of rows actually changed.

In other words, if you UPDATE but the values you set are already the values stored in the matching row, it does not count as a row affected.

This is the default behavior, but you can change this behavior if you set a PDO attribute when you connect. See PHP, MySQL - can you distinguish between rows matched and rows affected?