Moodle Filters - GROUP BY - moodle

Question

How can we get to work the moodle filters when GROUP BY - select form is used as filter mform field. I wasn't getting the desired output when I select the course. GROUP BY is not consider when sql_like function is called:
require_once($CFG->dirroot.'/filter_form.php');
$mform = new filter_form();
$coursefilter = '';
if ($formdata = $mform->get_data()) {
$coursefilter = $formdata->course;
}
$mform->set_data($formdata);
$mform->display();
$reporttable = new html_table();
$reporttable->head = array('course', 'users');
$reporttable->attributes['class'] = 'table';
$sql = "SELECT c.fullname, count(cc.userid) AS 'completed'
FROM {course_completions} cc JOIN {course} ON c.id = cc.course WHERE cc.timestarted > 0
GROUP BY c.fullname ";
$params = array();
if (!empty($coursefilter)) {
$params['fullname'] = '%' . $DB->sql_like_escape($coursefilter) . '%';
$sql .= " AND " . $DB->sql_like('c.fullname', ':fullname', false);
}
$mds = $DB->get_records_sql($sql, $params);
foreach ($mds as $m) {
$reporttable->data[] = new html_table_row(array(implode(array($m->fullname. $m->lastname)),
$m->completed ));
}
echo html_writer::table($reporttable);

Answer 1

Add the GROUP BY after the filter.
if (!empty($coursefilter)) {
$params['fullname'] = '%' . $DB->sql_like_escape($coursefilter) . '%';
$sql .= " AND " . $DB->sql_like('c.fullname', ':fullname', false);
}
$sql .= " GROUP BY c.fullname ";