Hierarchically sorted MySQL output with PHP - php

Question

I'm revising the navigation of my news system and would like to do so using minimal MySQL queries. I've managed to get it all down to one query, but something seems to be wrong. Any help would be greatly appreciated.
What I wish to achieve is (literally) the following overview of events, hierarchically sorted per year and month, along with the number of events in that month:
2012
--04 (3)
--02 (1)
--01 (1)
2011
--12 (3)
--11 (2)
--10 (3)
--09 (1)
--07 (1)
--02 (1)
I'm very close. My query is as follows:
SELECT start_date, date_format(start_date, "%Y") as year, date_format(start_date, "%m") as month FROM event ORDER BY start_date desc
Then, my PHP loop is as follows:
$year = '';
$year_counter = 0;
$month = '';
$month_counter = 1;
while($row = mysql_fetch_assoc($result)){
if ( $year != $row['year'] ) {
$year = $row['year'];
$output .= $year.'<br />';
}
if ( $month == $row['month'] ) {
$month_counter++;
} else {
$month = $row['month'];
$output .= '--'.$month.' ('.$month_counter.')<br />';
$month_counter = 1;
}
}
Which generates everything perfectly, except for the number of events per month, that seem to be always one line off (you please see the difference with the wanted result above).
2012
--04 (1)
--02 (3)
--01 (1)
2011
--12 (1)
--11 (3)
--10 (2)
--09 (3)
--07 (1)
--02 (1)
I've been tinkering with this all afternoon without success. I think it's best to leave it to the absolute experts. A hand please?

Answer 1

Currently, you're printing the month_counter before you've updated it for the next month. Before your while loop, you need to initialize your variables based on the first row retrieved rather than the default values.
if ($row = mysql_fetch_assoc($result){
$year = $row['year'];
$month = $row['month'];
$month_counter = 1; //1 because you've already counted the first article
// print out the first year
$output .= $year.'<br />';
while($row = mysql_fetch_assoc($result){
if ( $year != $row['year'] ) {
$year = $row['year'];
$output .= $year.'<br />';
}
if ( $month == $row['month'] ) {
// You've found one more article for this month, so increment the count
$month_counter++;
} else {
// You've hit a new month, so print out the information you collected
// about the previous month
$output .= '--'.$month.' ('.$month_counter.')<br />';
$month = $row['month'];
$month_counter = 1;
}
}
}
The difference between outputting the year and outputting the month, is that you also want to output the count associated with the month, whereas there is no additional information associated with the year. You have to print that before you change to the next month.

Answer 2

Your
$month = $row['month'];
is in the wrong place. It sets the $month-variable for a new month, but it has been counting the number for the months before it.
The first time it runs through the while-loop
if ( $month == $row['month'] )
can never be true, so it goes into the else-statement, displaying the month and the count (which is 1 because you set it to 1 at the top)...

Answer 3

I probably made some mistake here, but you could count events per Year-month and group them accordingly.. something like
SELECT start_date, date_format(start_date, "%Y") as year, date_format(start_date, "%m") as month, date_format(start_date, "%Y%m") gr, COUNT(id)
FROM event
ORDER BY start_date desc
GROUP BY gr