Deleting records based on row count and conditions - php

Question

I'm trying to create a quick-fix script in order to delete some records and get the data back on track.
Originally I had sales records inserting and using a quantity value to create an equal number of records. So I if I inserted a record with a quantity value of 12, then I would insert 12 of that record. This gave each SKU it's own record so that individual ones could have dates updated.
However, this has changed and I now need to do it based on store locations rather than quantity so I have too many records in some cases.
If I run the script with the current query (for dealer number 145) it selects all skus they have ordered this year, as expected. I need to now run a delete statement that takes a row count of each sku and compares it to the storefront value from the join.
So, if storefronts = 10 and there are 25 records for that sku/dealer combo, then I need to delete the oldest 15. The logic here is for each sku/dealer combo where curdate() < expire_date there should only be x number of rows equal to storefronts
I'm trying to test this with dealer 145, who has 10 stores. So for all records this year where curdate() is before the expiration, there should be no more than 10 records for each sku, if that makes sense.
$selectRecords = "
SELECT p.sku_id, p.dealer_id, p.start_date, p.expire_date, p.quantity, s.storefronts, s.dealer_id
FROM placements p
inner join storefronts s on p.dealer_id = s.dealer_id
WHERE p.dealer_id = 145
and start_date > '2018-01-01'
order by start_date asc;
";
try{
$currentRecords = $MysqlConn->prepare($selectRecords);
$currentResult = $currentRecords->execute();
$currentCount = $currentRecords->rowCount();
echo "Open Orders: " . $currentCount . "\n"; //returns correct count
}catch(PDOException $ex){
echo "QUERY FAILED!: " .$ex->getMessage();
}
$currentArray = [];
while($row = $selectRecords->fetch(PDO::FETCH_ASSOC)){
//pseudo code
foreach(sku_id){
if(rowCount > storefronts){
delete starting with oldest start_date
until row count == storefronts
}
}
}
I feel like it shouldn't be too complicated but I'm really stuck on how to execute this exactly.
Here's a fiddle with data examples:
http://sqlfiddle.com/#!9/c0dd6