How to display actual data from DB - php

Question

I´m doing SQL to display actual subject which is teaching currently by this and this teacher. It should displays only name of subject(f.e. it displays 'languages' at 8am at Teacher´s profile). In database I have table - timetable and there are data of start_time and end_time which are saved in DATETIME. I have problem how to interconnect SQL and PHP and then display.
I have this SQL query:
SELECT lessons.schoolday, lessons.start_time, lessons.end_time, lectors.lectorsurname, studentgroups.class_id, classes.grade, subjects.subjectname
FROM lessons INNER JOIN lectors ON lessons.lector_id=lectors.lector_id
INNER JOIN studentgroups ON lessons.studentgroup_id=studentgroups.studentgroup_id
INNER JOIN classes ON studentgroups.class_id=classes.class_id
INNER JOIN subjects ON lessons.subject_id=subjects.subject_id
WHERE lessons.start_time <= substring(('".date('Y-m-d H:i:s')."'),11,6)
AND lessons.end_time >= substring(('".date('Y-m-d H:i:s')."'),11,6)
AND lectors.lector_id=:id");
When I change date instead of interval(f.e. start_time->0000-00-00 08:00:00, end_time->0000-00-00 08:45:00), it is working. But in this way, it prints only Array(). HTML is displaying with Latte template and there is condition, if empty array, it displays message=Teacher is not teaching currently, but this is also not working.
.......
php code:
$stmt3 = $db->prepare(" SELECT l.schoolday, l.start_time, l.end_time, t.lectorsurname, sg.class_id, c.grade, s.subjectname
FROM lessons l
INNER JOIN lectors t ON l.lector_id=t.lector_id
INNER JOIN studentgroups sg ON l.studentgroup_id=sg.studentgroup_id
INNER JOIN classes c ON sg.class_id=c.class_id
INNER JOIN subjects s ON l.subject_id=s.subject_id
WHERE l.start_time <= CURTIME() AND l.end_time >= CURTIME() AND t.lector_id=:id
ORDER By c.grade, l.schoolday, l.start_time");
$stmt3->bindValue(":id", intval($_GET["id"]));
$stmt3->execute();
$data=$stmt3->fetchAll();
print_r($data);
$tplVars["lesson"] = $stmt3->fetchAll();
and latte template
<table>
.
.
.
<tr>
<th> Aktuálne vyučuje: </th>
</tr>
{foreach $lesson as $aktual}
{if !empty($aktual['grade'])}
<tr>
<td>{$aktual['grade']} </td>
</tr>
{/if}
{if ($aktual['grade']) == NULL}
<tr> <td> <span> Učiteľ momentálne nevyučuje </span></td></tr>
{/if}
{/foreach}
</table>

Answer 1

Search for some examples. with some aliases its better readable. Is a NOW() not enough? see this link for more MySql date and time functions
SELECT l.schoolday, l.start_time, l.end_time, t.lectorsurname, sg.class_id, c.grade, s.subjectname
FROM lessons l
INNER JOIN lectors t ON l.lector_id=t.lector_id
INNER JOIN studentgroups sg ON l.studentgroup_id=sg.studentgroup_id
INNER JOIN classes c ON sg.class_id=c.class_id
INNER JOIN subjects s ON l.subject_id=s.subject_id
WHERE l.start_time <= NOW() AND l.end_time >= NOW() AND t.lector_id=:id