After migrating any website from Joomla 3.x to Joomla 4.x, we encounter the aforementioned issue since Joomla 4.x no longer supports the query() method. Additionally, if a plugin is updated from a Joomla 3.x version to a Joomla 4.x version, this can also happen. In its place, we must use the execute() method. Examining the example code below, let me explain:
$db = & JFactory::getDBO(); $db->setQuery("SELECT * FROM TABLE_NAME"); $db->query();
For Joomla 3.x, the above code was sufficient, but for Joomla 4.x, we must use the following code.
$db = & JFactory::getDBO(); $db->setQuery("SELECT * FROM TABLE_NAME"); $db->execute();
because in the Joomla 4.x version, execute() substituted query() method.