query the lowest value for each day in the past 30 days in a table

Maybe the collection helper functions would be helpful?

https://laravel.com/docs/7.x/collections

You could possibly get all of the results for the month, then group them by the day, and then return the min value for the price key?

@drewdan Interesting. I'll look into it!

@alev You can do something like

$start = now()->subDays(30);

for ($i = 0; $i <= 30; $i++) {
    $days[] = $start->copy()->addDays($i)->toDateString();
}

$monthLabels = collect($days);

$month = Price::selectRaw('created_at as day, min(price) as price')->where('product_id', $product->id)->groupBy('day')->latest('day')->get()->mapWithKeys(function ($item) {
    return [$item['day'] => $item['price']];
});

$prices = $monthLabels->map(function ($day, $key) use ($month) {
    return $month->get($day, 0);
});

But I don't know your models and table structure, but propably it could help to you.

Thanks @michaloravec ! I'll look into that too.