Question

I have two table one is called licenses And One is called systems.
Now license table hold system id and license type (full or trial).
And systems table hold system mac_address.

Now one system may have more than one trial licenses and one full license.
Now i want to find systems whose full version haven’t generated yet with grouping them along with their mac_address .

Please little suggestion would be enough.

Answer 1

 select 
    s.*
from
    systems as s 
where
    s.system_id not in 
    (select l.system_id from licenses as l where l.licence_type='full')