Manage data in mysql according to dates.

I have a table of crockeries in which i have these columns

    id   name        units
    1    crockery1   100
    2    crockery2   100

And another table of events with these columns

    id   event_name   event_date
    1    event1       18-02-2018
    2    event2       18-02-2018
    3    event3       19-02-2018

Now I want to assign the crockeries to the events. Let's say that I assigned 20 units of crockery1 to event1 which is on date 18-02-1018. So when i assign crockery1 to event2 it should show me 80 units left because event2 is also on the same date as event1 but when i assign crockery1 to event3 it should show 100 units left because event3 is on different date,

So how could I acheive this functionality in PHP.

via Chebli Mohamed