SQlite: Select rows within a specific time range, ignoring the date - sqlite

Question

I have a table called messages that stores messages from a chat with the following columns: username, message, datetime, where the type of datetime is TEXT and it is stored in the following format: "yyyy/MM/dd hh:mm:ss". I want to retrieve the average count of rows within a specific time range, without bothering with the date. For instance:
SELECT avg(count(message))
FROM messages
WHERE datetime < "2016/mm/dd 13:00:00" AND
datetime > "2016/mm/dd 12:00:00"
Is there some operator that allows any character to take the place of "mm" and "dd". Essentially, I am trying to construct a query that retrieves the average amount of messages within a specific time range, not the amount of messages on a specific date.

Answer 1

If I read your question correctly, you want to use your WHERE clause to restrict to any calendar date in 2016 between 12 and 13 hours. In this case, you can use STRFTIME to extract the year and hour in string format from your datetime column.
SELECT COUNT(message)
FROM messages
WHERE STRFTIME('%Y', datetime) = '2016' AND
STRFTIME('%H', datetime) < '13' AND
STRFTIME('%H', datetime) > '12'
Note that the reason while the inequalities should work with strings is because numerical strings still sort based on their lexigraphical order.
Update:
Since your datetime column is in a non standard format, you may be able to workaround this by substringing off the various pieces you need to use in the WHERE clause:
SELECT COUNT(message)
FROM messages
WHERE SUBSTR(datetime, 1, 4) = '2016' AND
SUBSTR(datetime, 12, 2) < '13' AND
SUBSTR(datetime, 12, 2) > '12'