Calculate the average number of different words that appear on all pages whose title begins with A.
DIVIDE(SUM(words WHERE title = 'A%'), COUNT(words WHERE title = 'A%')) as percentage; A is a letter;
SELECT AVG(words) FROM pages WHERE title LIKE 'A%'
database name:db_id language_corpus
langs table langs Cols: language id dtype integer, language dtype text, locale dtype text, pages dtype integer, words dtype integer, 
pages table pages Cols: page id dtype integer, language id dtype integer, page dtype integer, revision dtype integer, title dtype text, words dtype integer, 
words table words Cols: word id dtype integer, word dtype text, occurrences dtype integer, 
langs_words table langs_words Cols: language id dtype integer, word id dtype integer, occurrences dtype integer, 
pages_words table pages_words Cols: page id dtype integer, word id dtype integer, occurrences dtype integer, 
biwords table biwords Cols: language id dtype integer, word id of the first word dtype integer, word id of the second word dtype integer, occurrences dtype integer, 
