You are now a sqlite data analyst, and you are given a database schema as follows:

    【Schema】
    【DB_ID】 books
【Schema】
# Table: book_language
[
(language_id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(language_code:TEXT, Examples: [eng, en-US, fre]),
(language_name:TEXT, Examples: [English])
]
# Table: country
[
(country_id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(country_name:TEXT, Examples: [Afghanistan, Netherlands Antilles, Albania])
]
# Table: customer
[
(customer_id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(first_name:TEXT, Examples: [Ursola, Ruthanne, Reidar]),
(last_name:TEXT, Examples: [Purdy, Vatini, Turbitt]),
(email:TEXT)
]
# Table: order_history
[
(history_id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(order_id:INTEGER, Examples: [1, 2, 3]),
(status_id:INTEGER, Examples: [1, 2, 3]),
(status_date:DATETIME, Examples: [2021-07-14 17:04:28])
]
# Table: book
[
(book_id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(title:TEXT, Examples: [The World's First Love: Mary  Mother of God]),
(isbn13:TEXT, Examples: [8987059752, 20049130001, 23755004321]),
(language_id:INTEGER, Examples: [2, 1, 5]),
(num_pages:INTEGER, Examples: [276, 352, 128]),
(publication_date:DATE, Examples: [1996-09-01]),
(publisher_id:INTEGER, Examples: [1010, 1967, 1978])
]
# Table: book_author
[
(book_id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(author_id:INTEGER, Primary Key, Examples: [1, 2, 3])
]
# Table: shipping_method
[
(method_id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(method_name:TEXT, Examples: [Standard, Priority, Express]),
(cost:REAL, Examples: [5.9, 8.9, 11.9])
]
# Table: order_line
[
(line_id:INTEGER, Primary Key, Examples: [1024, 1025, 1026]),
(order_id:INTEGER, Examples: [2051, 899, 4994]),
(book_id:INTEGER, Examples: [10720, 10105, 6503]),
(price:REAL, Examples: [3.19, 1.24, 14.74])
]
# Table: address
[
(address_id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(street_number:TEXT, Examples: [57, 86, 292]),
(street_name:TEXT, Examples: [Glacier Hill Avenue, Dottie Junction, Ramsey Avenue]),
(city:TEXT, Examples: [Torbat-e Jām, Beaumont, Cayambe]),
(country_id:INTEGER, Examples: [95, 37, 60])
]
# Table: publisher
[
(publisher_id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(publisher_name:TEXT, Examples: [10/18, 1st Book Library, 1st World Library])
]
# Table: author
[
(author_id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(author_name:TEXT, Examples: [A. Bartlett Giamatti, A. Elizabeth Delany, A. Merritt])
]
# Table: address_status
[
(status_id:INTEGER, Primary Key, Examples: [1, 2]),
(address_status:TEXT, Examples: [Active, Inactive])
]
# Table: cust_order
[
(order_id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(order_date:DATETIME, Examples: [2021-07-14 10:47:19]),
(customer_id:INTEGER, Examples: [387, 1256, 1335]),
(shipping_method_id:INTEGER, Examples: [4, 2, 1]),
(dest_address_id:INTEGER, Examples: [1, 2, 3])
]
# Table: customer_address
[
(customer_id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(address_id:INTEGER, Primary Key, Examples: [606, 266, 376]),
(status_id:INTEGER, Examples: [1, 2])
]
# Table: order_status
[
(status_id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(status_value:TEXT, Examples: [Order Received, Pending Delivery, Delivery In Progress])
]
【Foreign keys】
order_history.status_id=order_status.status_id
order_history.order_id=cust_order.order_id
book.language_id=book_language.language_id
book.publisher_id=publisher.publisher_id
book_author.author_id=author.author_id
book_author.book_id=book.book_id
order_line.book_id=book.book_id
order_line.order_id=cust_order.order_id
address.country_id=country.country_id
cust_order.dest_address_id=address.address_id
cust_order.shipping_method_id=shipping_method.method_id
cust_order.customer_id=customer.customer_id
customer_address.address_id=address.address_id
customer_address.customer_id=customer.customer_id

    【Question】
    What is the average price for the order line? average price refers to AVG(price)

    【Evidence】
    average price refers to AVG(price)

    Please read and understand the database schema carefully, and generate an executable SQL based on the user's question and evidence. 

SQL: SELECT AVG(price) FROM order_line