PHP Array Merge Issue - php

Question

I have a table of races that have the race name, race id, and race date.
I am trying to build a single array (it has to be a single array returned via a function call) which would contain a list of the races in the following format:
,,---2017---
The Resolution AR, 58, 1.14.2017
Heartbreaker AR, 59, 2.11.2017
,,---2016---
The Blue Ridge AR, 38, 5.21.2016
The Fathers Day AR, 43, 6.18.2016
Adventure Bike (Santos), 54, 7.30.2016
,,---2015---
Gemini Springs AR, 4, 12.14.2015
I am almost there! But I am having one issue.
This is the current code I have:
function get_races() {
// get all the years that have races
$years = $wpdb->get_results("
select DATE_FORMAT(r.race_date,'%Y') year
from race_calendar r
group by DATE_FORMAT(r.race_date,'%Y')
order by DATE_FORMAT(r.race_date,'%Y') desc;
");
// loop through all years that have races
foreach ( $years as $year ) {
// add year header to array
$year_header = array(array ('','','---'.$year->year.'---'));
// get races for this particular year
$races = $wpdb->get_results("
select r.race_name
,r.race_id
,date_format(r.race_date,'%c.%d.%Y') race_date
from race_calendar r
where DATE_FORMAT(r.race_date,'%Y') = ".$year->year."
order by r.race_date;
", ARRAY_N);
// merge the year header and the races into an array
$merged_arr = array_merge($year_header, $races);
}
return $merged_arr;
}
// call function to get list of races
$races = get_races();
// display the list of races (with the year separator)
foreach ( $races as $race )
{
echo $race['0'] . ',' . $race['1'] . ',' . $race['2'] . '<br />';
}
It works. But problem is, that code above only displays the last iteration of the years loop, in this case, 2015:
,,---2015---
Gemini Springs AR, 4, 12.14.2015
Obviously $merged_arr is begin reset with each iteration of the years loop
How can I update it so that the resulting array in the function contains the data for all the iterations of the years loop?

Answer 1

You can do this all with a single query. Just select all the rows, then loop over the results and detect when the year changes from the previous iteration to know when to output your separator row.
$last = null;
$query = <select * from race_calendar order by race_date>
foreach ($query as $row) {
$year = // year of $row['race_date']
if ($year != $last) {
// new year, output separator line
$last = $year;
}
// output data line
}