Solve the following sql problem:
How many customers are active?

Schema:
SCHEMA:
- Table: film_text
  - Column: film_id
    - Samples: [1, 2, 3, 4, 5]
  - Column: title
    - Samples: [ACADEMY DINOSAUR, ACE GOLDFINGER, ADAPTATION HOLES, AFFAIR PREJUDICE, AFRICAN EGG]
  - Column: description
    - Samples: [A Epic Drama of a Feminist And a Mad Scientist who must Battle a Teach..., A Astounding Epistle of a Database Administrator And a Explorer who mu..., A Astounding Reflection of a Lumberjack And a Car who must Sink a Lumb..., A Fanciful Documentary of a Frisbee And a Lumberjack who must Chase a ..., A Fast-Paced Documentary of a Pastry Chef And a Dentist who must Pursu... (truncated)]
- Table: actor
  - Column: actor_id
    - Samples: [1, 2, 3, 4, 5]
  - Column: first_name
    - Samples: [PENELOPE, NICK, ED, JENNIFER, JOHNNY]
  - Column: last_name
    - Samples: [GUINESS, WAHLBERG, CHASE, DAVIS, LOLLOBRIGIDA]
  - Column: last_update
    - Samples: [2006-02-15 04:34:33.0, 2006-02-15 04:34:33.0, 2006-02-15 04:34:33.0, 2006-02-15 04:34:33.0, 2006-02-15 04:34:33.0]
- Table: address
  - Column: address_id
    - Samples: [1, 2, 3, 4, 5]
  - Column: address
    - Samples: [47 MySakila Drive, 28 MySQL Boulevard, 23 Workhaven Lane, 1411 Lillydale Drive, 1913 Hanoi Way]
  - Column: address2
    - Samples: [None, None, None, None, ]
  - Column: district
    - Samples: [Alberta, QLD, Alberta, QLD, Nagasaki]
  - Column: city_id
    - Samples: [300, 576, 300, 576, 463]
  - Column: postal_code
    - Samples: [, , , , 35200]
  - Column: phone
    - Samples: [, , 14033335568, 6172235589, 28303384290]
  - Column: last_update
    - Samples: [2006-02-15 04:45:30.0, 2006-02-15 04:45:30.0, 2006-02-15 04:45:30.0, 2006-02-15 04:45:30.0, 2006-02-15 04:45:30.0]
- Table: category
  - Column: category_id
    - Samples: [1, 2, 3, 4, 5]
  - Column: name
    - Samples: [Action, Animation, Children, Classics, Comedy]
  - Column: last_update
    - Samples: [2006-02-15 04:46:27.0, 2006-02-15 04:46:27.0, 2006-02-15 04:46:27.0, 2006-02-15 04:46:27.0, 2006-02-15 04:46:27.0]
- Table: city
  - Column: city_id
    - Samples: [1, 2, 3, 4, 5]
  - Column: city
    - Samples: [A Corua (La Corua), Abha, Abu Dhabi, Acua, Adana]
  - Column: country_id
    - Samples: [87, 82, 101, 60, 97]
  - Column: last_update
    - Samples: [2006-02-15 04:45:25.0, 2006-02-15 04:45:25.0, 2006-02-15 04:45:25.0, 2006-02-15 04:45:25.0, 2006-02-15 04:45:25.0]
- Table: country
  - Column: country_id
    - Samples: [1, 2, 3, 4, 5]
  - Column: country
    - Samples: [Afghanistan, Algeria, American Samoa, Angola, Anguilla]
  - Column: last_update
    - Samples: [2006-02-15 04:44:00.0, 2006-02-15 04:44:00.0, 2006-02-15 04:44:00.0, 2006-02-15 04:44:00.0, 2006-02-15 04:44:00.0]
- Table: customer
  - Column: customer_id
    - Samples: [1, 2, 3, 4, 5]
  - Column: store_id
    - Samples: [1, 1, 1, 2, 1]
  - Column: first_name
    - Samples: [MARY, PATRICIA, LINDA, BARBARA, ELIZABETH]
  - Column: last_name
    - Samples: [SMITH, JOHNSON, WILLIAMS, JONES, BROWN]
  - Column: email
    - Samples: [MARY.SMITH@sakilacustomer.org, PATRICIA.JOHNSON@sakilacustomer.org, LINDA.WILLIAMS@sakilacustomer.org, BARBARA.JONES@sakilacustomer.org, ELIZABETH.BROWN@sakilacustomer.org]
  - Column: address_id
    - Samples: [5, 6, 7, 8, 9]
  - Column: active
    - Samples: [1, 1, 1, 1, 1]
  - Column: create_date
    - Samples: [2006-02-14 22:04:36.0, 2006-02-14 22:04:36.0, 2006-02-14 22:04:36.0, 2006-02-14 22:04:36.0, 2006-02-14 22:04:36.0]
  - Column: last_update
    - Samples: [2006-02-15 04:57:20.0, 2006-02-15 04:57:20.0, 2006-02-15 04:57:20.0, 2006-02-15 04:57:20.0, 2006-02-15 04:57:20.0]
- Table: film
  - Column: film_id
    - Samples: [1, 2, 3, 4, 5]
  - Column: title
    - Samples: [ACADEMY DINOSAUR, ACE GOLDFINGER, ADAPTATION HOLES, AFFAIR PREJUDICE, AFRICAN EGG]
  - Column: description
    - Samples: [A Epic Drama of a Feminist And a Mad Scientist who must Battle a Teach..., A Astounding Epistle of a Database Administrator And a Explorer who mu..., A Astounding Reflection of a Lumberjack And a Car who must Sink a Lumb..., A Fanciful Documentary of a Frisbee And a Lumberjack who must Chase a ..., A Fast-Paced Documentary of a Pastry Chef And a Dentist who must Pursu... (truncated)]
  - Column: release_year
    - Samples: [2006, 2006, 2006, 2006, 2006]
  - Column: language_id
    - Samples: [1, 1, 1, 1, 1]
  - Column: original_language_id
    - Samples: [None, None, None, None, None]
  - Column: rental_duration
    - Samples: [6, 3, 7, 5, 6]
  - Column: rental_rate
    - Samples: [0.99, 4.99, 2.99, 2.99, 2.99]
  - Column: length
    - Samples: [86, 48, 50, 117, 130]
  - Column: replacement_cost
    - Samples: [20.99, 12.99, 18.99, 26.99, 22.99]
  - Column: rating
    - Samples: [PG, G, NC-17, G, G]
  - Column: special_features
    - Samples: [Deleted Scenes,Behind the Scenes, Trailers,Deleted Scenes, Trailers,Deleted Scenes, Commentaries,Behind the Scenes, Deleted Scenes]
  - Column: last_update
    - Samples: [2006-02-15 05:03:42.0, 2006-02-15 05:03:42.0, 2006-02-15 05:03:42.0, 2006-02-15 05:03:42.0, 2006-02-15 05:03:42.0]
- Table: film_actor
  - Column: actor_id
    - Samples: [1, 1, 1, 1, 1]
  - Column: film_id
    - Samples: [1, 23, 25, 106, 140]
  - Column: last_update
    - Samples: [2006-02-15 05:05:03.0, 2006-02-15 05:05:03.0, 2006-02-15 05:05:03.0, 2006-02-15 05:05:03.0, 2006-02-15 05:05:03.0]
- Table: film_category
  - Column: film_id
    - Samples: [1, 2, 3, 4, 5]
  - Column: category_id
    - Samples: [6, 11, 6, 11, 8]
  - Column: last_update
    - Samples: [2006-02-15 05:07:09.0, 2006-02-15 05:07:09.0, 2006-02-15 05:07:09.0, 2006-02-15 05:07:09.0, 2006-02-15 05:07:09.0]
- Table: inventory
  - Column: inventory_id
    - Samples: [1, 2, 3, 4, 5]
  - Column: film_id
    - Samples: [1, 1, 1, 1, 1]
  - Column: store_id
    - Samples: [1, 1, 1, 1, 2]
  - Column: last_update
    - Samples: [2006-02-15 05:09:17.0, 2006-02-15 05:09:17.0, 2006-02-15 05:09:17.0, 2006-02-15 05:09:17.0, 2006-02-15 05:09:17.0]
- Table: language
  - Column: language_id
    - Samples: [1, 2, 3, 4, 5]
  - Column: name
    - Samples: [English, Italian, Japanese, Mandarin, French]
  - Column: last_update
    - Samples: [2006-02-15 05:02:19.0, 2006-02-15 05:02:19.0, 2006-02-15 05:02:19.0, 2006-02-15 05:02:19.0, 2006-02-15 05:02:19.0]
- Table: payment
  - Column: payment_id
    - Samples: [1, 2, 3, 4, 5]
  - Column: customer_id
    - Samples: [1, 1, 1, 1, 1]
  - Column: staff_id
    - Samples: [1, 1, 1, 2, 2]
  - Column: rental_id
    - Samples: [76, 573, 1185, 1422, 1476]
  - Column: amount
    - Samples: [2.99, 0.99, 5.99, 0.99, 9.99]
  - Column: payment_date
    - Samples: [2005-05-25 11:30:37.0, 2005-05-28 10:35:23.0, 2005-06-15 00:54:12.0, 2005-06-15 18:02:53.0, 2005-06-15 21:08:46.0]
  - Column: last_update
    - Samples: [2006-02-15 22:12:30.0, 2006-02-15 22:12:30.0, 2006-02-15 22:12:30.0, 2006-02-15 22:12:30.0, 2006-02-15 22:12:30.0]
- Table: rental
  - Column: rental_id
    - Samples: [1, 2, 3, 4, 5]
  - Column: rental_date
    - Samples: [2005-05-24 22:53:30.0, 2005-05-24 22:54:33.0, 2005-05-24 23:03:39.0, 2005-05-24 23:04:41.0, 2005-05-24 23:05:21.0]
  - Column: inventory_id
    - Samples: [367, 1525, 1711, 2452, 2079]
  - Column: customer_id
    - Samples: [130, 459, 408, 333, 222]
  - Column: return_date
    - Samples: [2005-05-26 22:04:30.0, 2005-05-28 19:40:33.0, 2005-06-01 22:12:39.0, 2005-06-03 01:43:41.0, 2005-06-02 04:33:21.0]
  - Column: staff_id
    - Samples: [1, 1, 1, 2, 1]
  - Column: last_update
    - Samples: [2006-02-15 21:30:53.0, 2006-02-15 21:30:53.0, 2006-02-15 21:30:53.0, 2006-02-15 21:30:53.0, 2006-02-15 21:30:53.0]
- Table: staff
  - Column: staff_id
    - Samples: [1, 2]
  - Column: first_name
    - Samples: [Mike, Jon]
  - Column: last_name
    - Samples: [Hillyer, Stephens]
  - Column: address_id
    - Samples: [3, 4]
  - Column: picture
    - Samples: [0x3F504E470D0A1A0A0000000D4948445200000079000000750802000000E55AD96500..., None (truncated)]
  - Column: email
    - Samples: [Mike.Hillyer@sakilastaff.com, Jon.Stephens@sakilastaff.com]
  - Column: store_id
    - Samples: [1, 2]
  - Column: active
    - Samples: [1, 1]
  - Column: username
    - Samples: [Mike, Jon]
  - Column: password
    - Samples: [8cb2237d0679ca88db6464eac60da96345513964, 8cb2237d0679ca88db6464eac60da96345513964]
  - Column: last_update
    - Samples: [2006-02-15 04:57:16.0, 2006-02-15 04:57:16.0]
- Table: store
  - Column: store_id
    - Samples: [1, 2]
  - Column: manager_staff_id
    - Samples: [1, 2]
  - Column: address_id
    - Samples: [1, 2]
  - Column: last_update
    - Samples: [2006-02-15 04:57:12.0, 2006-02-15 04:57:12.0]

SELECT COUNT(customer_id) FROM customer WHERE active = 1