Complex Database mysql…
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I have an Art Gallery project…..

Every hour a group visit gallery, 
which means 24 hours 24 groups.

Some time it becomes more then 24 groups like 25,28,30,40 ….
Every group has 50 to 60 or 70 visitors with Unique ID’s generated by the system
I have to design a database in which I can insert all group ID’s according to the hour visit
Like :

1 hour = 1,34,3,6,67,53,57,………………………..up to 60 or 70 total ID’s
2 hour= 2,35,4,7,68,54,58…………………………... up to 60 or 70 total ID’s
And so on…..for a day and next day repeat the same process with other unique ID’s.

If I create a table for hours then I got NULL values for other hours which means useless space!
If I create different tables for hours then what if I got more than the number of tables I have?

Is anyone suggesting me how to design a perfect table or some other way to insert values without NULL values?
I am using PHP with mysql. Any help will be appreciated