PHP-MYSQL：最近12个月到每个月的最后一天

Question

A project I am on has the need to get an average invoice total for each of the the last 12 months. I can easily get what I need by doing 12 queries (1 for each month), but its very ugly, I end up with 12 unique variables(id rather have a loop ), and I know there is a better way.

Can anyone help with the best way to get the following:

SELECT AVG(invoice_total) FROM invoice WHERE date between '2015-01-01' AND '2015-01-31'
SELECT AVG(invoice_total) FROM invoice WHERE date between '2015-02-01' AND '2015-02-28'
SELECT AVG(invoice_total) FROM invoice WHERE date between '2015-03-01' AND '2015-03-31'

etc...

Im plotting these on a graph, so I need a data point for each month.

End result would be something like:

Jan: $2323
Feb: $3523
March: $6453

ect... but would start 12 months ago from the current month.

Thank you.

PS For refrence, this is how I am plotting the last 90 days:

$get_unconfirmed_appointments = "
SELECT total
     , invoice_date 
  FROM invoice 
 WHERE clinic_id = 20
   AND invoice_date >= '$date' 
   AND invoice_date <= '$date_two' 
 ORDER 
    BY invoice_date ASC
";
        $result = $conn->query($get_unconfirmed_appointments) or die($conn->error.__LINE__);    
            while($row = $result->fetch_assoc()) {
                    $totals[$row['invoice_date']][] = $row['total'];
            }
    $sub_arrays = array_chunk($totals, 3);
    foreach ($sub_arrays as $threedays) {
        foreach ($threedays as $value) {
            foreach ($value as $val) {
                $all[] = $val;
            }                                   
        }
        $average = array_sum($all) / count($all);
        $data_point=round($average,2);
        plot($data_point);
    }

I need the same idea as above, but for the last 12 months. Average for each month.

Answer 1

You can use the MONTHNAME function and group by that:

http://dev.mysql.com/doc/refman/5.5/en/date-and-time-functions.html#function_month

You SQL will be something like that:

SELECT AVG(invoice_total), MONTHNAME(invoice_date)  FROM invoice WHERE invoice_date BETWEEN '2014-11-11'  AND '2015-02-09' GROUP BY MONTHNAME(invoice_date)