Grouping data to get reports by intervals - php

Question

I posted a question some time ago on representing data per date horizontally on a datatable.
See here: datatables dates at the top and data cells going from left to right
With the help of that thread I was able to get the data to display how I wanted it. With the dates showing at the top, the service provided on the left and all data associated with any date between the 2 date paramters inside the main body. (If there is no data in a particular date then the < td > will display 0. See here:
http://www.phpwin.org/s/ewbAS6
After manipulating this code further I made the dates of the search dynamic by proving a form with a start date and an end date, and a dropdown with the options of:
Daily
Weekly
Monthly
Quaterly
Yearly
this allows the interval of dates at the top to become dynamic. Of course all this is doing is changing the value of the 2nd parameter inside the date while loop.
WHILE (strtotime($date) <= strtotime($end_date)) {
echo '<th>' . $date . '</th>';
$date = date('Y-m-d', strtotime($date . ' +1day'));
}
with the parameter set at Weekly, the value of +1day becomes +1week, at Monthly; the value becomes +1month and so on.
MY ISSUE:
When the interval is set to daily, the dates with their corresponding attendance counts are displayed correctly but once you try to increase the interval to +1week and above the data does not round up to the week shown. Check this:
[LINK1]Per day: http://www.phpwin.org/s/ewbAS6
[LINK2]Per month: http://www.phpwin.org/s/xRo3I6
Looking at the array (modified on the LINK2)
$result[] = array('Service Name' => 'Health', 'date' => '2017-04-04', 'Attendance' => 5);
$result[] = array('Service Name' => 'Payroll', 'date' => '2017-04-16', 'Attendance' => 5);
$result[] = array('Service Name' => 'Saturday Youth Meeting', 'date' => '2017-04-03', 'Attendance' => 1);
$result[] = array('Service Name' => 'Saturday Youth Meeting', 'date' => '2017-05-03', 'Attendance' => 3);
$result[] = array('Service Name' => 'Payroll', 'date' => '2017-05-03', 'Attendance' => 2);
$result[] = array('Service Name' => 'Payroll', 'date' => '2017-04-11', 'Attendance' => 3);
$result[] = array('Service Name' => 'Payroll', 'date' => '2018-04-03', 'Attendance' => 10);
You can see in the array that there are multiple attendance entries in April, totaling 14 Attendances in that month however during LINK2 where the interval is increased to a month instead of showing 14 for April (which would be the sum of all the dates in that particular month) it shows the value 1.
My live version takes the array from a database so I used the YEAR(), MONTH(), WEEK() and DAY() function on the date and used group by. The query executes how I want it but having issues working on the PHP end.