Checking for maximum length of consecutive days which satisfy specific condition - mysql

Question

I have a MySQL table with the structure:
beverages_log(id, users_id, beverages_id, timestamp)
I'm trying to compute the maximum streak of consecutive days during which a user (with id 1) logs a beverage (with id 1) at least 5 times each day. I'm pretty sure that this can be done using views as follows:
CREATE or REPLACE VIEW daycounts AS
SELECT count(*) AS n, DATE(timestamp) AS d FROM beverages_log
WHERE users_id = '1' AND beverages_id = 1 GROUP BY d;
CREATE or REPLACE VIEW t AS SELECT * FROM daycounts WHERE n >= 5;
SELECT MAX(streak) AS current FROM ( SELECT DATEDIFF(MIN(c.d), a.d)+1 AS streak
FROM t AS a LEFT JOIN t AS b ON a.d = ADDDATE(b.d,1)
LEFT JOIN t AS c ON a.d <= c.d
LEFT JOIN t AS d ON c.d = ADDDATE(d.d,-1)
WHERE b.d IS NULL AND c.d IS NOT NULL AND d.d IS NULL GROUP BY a.d) allstreaks;
However, repeatedly creating views for different users every time I run this check seems pretty inefficient. Is there a way in MySQL to perform this computation in a single query, without creating views or repeatedly calling the same subqueries a bunch of times?

Answer 1

This solution seems to perform quite well as long as there is a composite index on users_id and beverages_id -
SELECT *
FROM (
SELECT t.*, IF(#prev + INTERVAL 1 DAY = t.d, #c := #c + 1, #c := 1) AS streak, #prev := t.d
FROM (
SELECT DATE(timestamp) AS d, COUNT(*) AS n
FROM beverages_log
WHERE users_id = 1
AND beverages_id = 1
GROUP BY DATE(timestamp)
HAVING COUNT(*) >= 5
) AS t
INNER JOIN (SELECT #prev := NULL, #c := 1) AS vars
) AS t
ORDER BY streak DESC LIMIT 1;

Answer 2

Why not include user_id in they daycounts view and group by user_id and date.
Also include user_id in view t.
Then when you are queering against t add the user_id to the where clause.
Then you don't have to recreate your views for every single user you just need to remember to include in your where clause.

Answer 3

That's a little tricky. I'd start with a view to summarize events by day:
CREATE VIEW BView AS
SELECT UserID, BevID, CAST(EventDateTime AS DATE) AS EventDate, COUNT(*) AS NumEvents
FROM beverages_log
GROUP BY UserID, BevID, CAST(EventDateTime AS DATE)
I'd then use a Dates table (just a table with one row per day; very handy to have) to examine all possible date ranges and throw out any with a gap. This will probably be slow as hell, but it's a start:
SELECT
UserID, BevID, MAX(StreakLength) AS StreakLength
FROM
(
SELECT
B1.UserID, B1.BevID, B1.EventDate AS StreakStart, DATEDIFF(DD, StartDate.Date, EndDate.Date) AS StreakLength
FROM
BView AS B1
INNER JOIN Dates AS StartDate ON B1.EventDate = StartDate.Date
INNER JOIN Dates AS EndDate ON EndDate.Date > StartDate.Date
WHERE
B1.NumEvents >= 5
-- Exclude this potential streak if there's a day with no activity
AND NOT EXISTS (SELECT * FROM Dates AS MissedDay WHERE MissedDay.Date > StartDate.Date AND MissedDay.Date <= EndDate.Date AND NOT EXISTS (SELECT * FROM BView AS B2 WHERE B1.UserID = B2.UserID AND B1.BevID = B2.BevID AND MissedDay.Date = B2.EventDate))
-- Exclude this potential streak if there's a day with less than five events
AND NOT EXISTS (SELECT * FROM BView AS B2 WHERE B1.UserID = B2.UserID AND B1.BevID = B2.BevID AND B2.EventDate > StartDate.Date AND B2.EventDate <= EndDate.Date AND B2.NumEvents < 5)
) AS X
GROUP BY
UserID, BevID