-- Database schema
| Breeds : breed_code [ TEXT ] primary_key , breed_name [ TEXT ] | Charges : charge_id [ INT ] primary_key , charge_type [ TEXT ] , charge_amount [ INT ] | Sizes : size_code [ TEXT ] primary_key , size_description [ TEXT ] | Treatment_Types : treatment_type_code [ TEXT ] primary_key , treatment_type_description [ TEXT ] | Owners : owner_id [ INT ] primary_key , first_name [ TEXT ] , last_name [ TEXT ] , street [ TEXT ] , city [ TEXT ] , state [ TEXT ] , zip_code [ TEXT ] , email_address [ TEXT ] , home_phone [ TEXT ] , cell_number [ TEXT ] | Dogs : dog_id [ INT ] primary_key , owner_id [ INT ] Dogs.owner_id = Owners.owner_id , abandoned_yn [ TEXT ] , breed_code [ TEXT ] Dogs.breed_code = Breeds.breed_code , size_code [ TEXT ] Dogs.size_code = Sizes.size_code , name [ TEXT ] , age [ TEXT ] , date_of_birth [ TEXT ] , gender [ TEXT ] , weight [ TEXT ] , date_arrived [ TEXT ] , date_adopted [ TEXT ] , date_departed [ TEXT ] | Professionals : professional_id [ INT ] primary_key , role_code [ TEXT ] , first_name [ TEXT ] , street [ TEXT ] , city [ TEXT ] , state [ TEXT ] , zip_code [ TEXT ] , last_name [ TEXT ] , email_address [ TEXT ] , home_phone [ TEXT ] , cell_number [ TEXT ] | Treatments : treatment_id [ INT ] primary_key , dog_id [ INT ] Treatments.dog_id = Dogs.dog_id , professional_id [ INT ] Treatments.professional_id = Professionals.professional_id , treatment_type_code [ TEXT ] Treatments.treatment_type_code = Treatment_Types.treatment_type_code , date_of_treatment [ TEXT ] , cost_of_treatment [ INT ] |
-- -- Compute the average age of all the dogs.

SELECT avg(age) FROM Dogs;