Show all the guests information.
select * from guests
How many genders are there in total?
select count(distinct gender_code) from guests
Has "Rebeca" ever visited, show the related information.
select * from guests where guest_first_name = "Rebeca"
Count how many guests for each gender, and list them in descending order.
select gender_code, count(*) from guests group by gender_code order by count(*) desc