Ask everyone for an SQL statement, more points.

Select count (room id) from the room type table as

Leave the online table as b on b.id=a.id

The left connector is C. ID = C on B. ID.

Whether the check-in time is free or not depends on whether the check-in time and check-out time of the offline reservation repeat with you and how many rooms are left.

Let me give you a general idea. Write your own sentences.