Efficient query to just return row count - php

Question

I have five different queries running on my about page showing basic data like the number of news stories we have on the site. I am using queries like this:
$sql4 = "SELECT `ride_id` FROM `tpf_rides` WHERE `type` LIKE '%Roller Coaster%'" ;
$result4 = $pdo->query($sql4);
$coasters = $result4->rowCount();
but wonder if there is a more efficient way. I've tried to minimize the load by only pulling id's but because I only need the count can the load be lightened even more?
Also these queries only really need to run once or twice per day, not every time the page is loaded. Can someone point me in the direction of setting this up? I've never had to do this before. Thanks.

Answer 1

Yes there is a more efficient way. Let the database do the counting for you:
SELECT count(*) as cnt
FROM `tpf_rides`
WHERE `type` LIKE '%Roller Coaster%';
If all the counts you are looking for are from the tpf_rides table, then you can do them in one query:
SELECT sum(`type` LIKE '%Roller Coaster%') as RollerCoaster,
sum(`type` LIKE '%Haunted House%') as HauntedHouse,
sum(`type` LIKE '%Ferris Wheel%') as FerrisWheel
FROM `tpf_rides`;
That would be even faster than running three different queries.

Answer 2

If you want to run those queries only every now and then you need to keep the result stored somewhere. This can take a form of a pre-calculated sum you manage yourself or a simple cache.
Below is a very simple and naive cache implementation that should work reliably on linux. Many things can be improved here but maybe this will give you an idea of what you could do.
The below is not compatible with the query suggested by Gordon Linoff which returns multiple counts.
The code has not been tested.
$cache_directory = "/tmp/";
$cache_lifetime = 86400; // time to keep cache in seconds. 24 hours = 86400sec
$sql4 = "SELECT count(*) FROM `tpf_rides` WHERE `type` LIKE '%Roller Coaster%'";
$cache_key = md5($sql4); //generate a semi-unique identifier for the query
$cache_file = $cache_directory . $cache_key; // generate full cache file path
if (!file_exists($cache_file) || time() <= strtotime(filemtime($cache)) + $cache_lifetime)
{
// cache file doesn't exist or has expired
$result4 = $pdo->query($sql4);
$coasters = $result4->fetchColumn();
file_put_contents($cache_file, $coasters); // store the result in a cache file
} else {
// file exists and data is up to date
$coasters = file_get_contents($cache_file);
}
I would strongly suggest you break this down into functions that take care of different aspects of the problem.