Prøv at ændre det, der kan lide...
count(select * from bookings where b.id_customer = c.id)
...til...
(select count(*) from bookings where b.id_customer = c.id)
Prøv at ændre det, der kan lide...
count(select * from bookings where b.id_customer = c.id)
...til...
(select count(*) from bookings where b.id_customer = c.id)