Mysql - get results from complex criteria - mysql

Question

I have database with statistics over a number of websites and I'm currently having an issue with a rather complex query that I have no idea how to do (or if it's even possible).
I have 2 tables: websites and visits. The former is a list of all websites and their properties, while the former is a list of each user's visit on a specific website.
The program I'm making is supposed to fetch websites that need to be "scanned". The interval between each scan for each site depends on the websites total number of visits for the last 30 days. Here is a table with the intended scan-interval:
The tables have the following structure:
Websites
Visits
What I want is a query that returns the websites that are either at or past their individual update deadline (can be seen from the last_scanned column).
Is this easily doable in a single query?

Answer 1

Here's something you can try:
SELECT main.*
FROM (
SELECT
w.web_id,
w.url,
w.last_scanned,
(SELECT COUNT(*)
FROM visits v
WHERE v.web_id = w.web_id
AND TIMESTAMPDIFF(DAY,v.added_on, NOW()) <=30
) AS visit_count,
TIMESTAMPDIFF(HOUR,w.last_scanned, NOW()) AS hrs_since_update
FROM websites w
) main
WHERE
(CASE
WHEN visit_count >= 0 AND visit_count <= 10 AND hrs_since_update >= 4320 THEN 1
WHEN visit_count >= 11 AND visit_count <= 100 AND hrs_since_update >= 2160 THEN 1
WHEN visit_count >= 101 AND visit_count <= 500 AND hrs_since_update >= 1080 THEN 1
WHEN visit_count >= 501 AND visit_count <= 1000 AND hrs_since_update >= 720 THEN 1
WHEN visit_count >= 1001 AND visit_count <= 2000 AND hrs_since_update >= 360 THEN 1
WHEN visit_count >= 2001 AND visit_count <= 5000 AND hrs_since_update >= 168 THEN 1
WHEN visit_count >= 5001 AND visit_count <= 10000 AND hrs_since_update >= 72 THEN 1
WHEN visit_count >= 10001 AND hrs_since_update >= 24 THEN 1
ELSE 0
END) = 1;
Here's the fiddle demo: http://sqlfiddle.com/#!9/1f671/1

Answer 2

First, I would make a subquery to get the visit counts from the visits table for each distinct web_id. Then, LEFT OUTER JOIN the websites table to this subquery. You can then query the result for each possible condition in your visits-to-update-frequency table, like so:
SELECT websites.* FROM websites
LEFT OUTER JOIN (
SELECT visits.web_id, COUNT(*) AS visits_count FROM visits GROUP BY visits.web_id
) v ON v.web_id = websites.web_id
WHERE
(v.visits_count <= 10 AND websites.last_scanned <= DATE_SUB(NOW(), INTERVAL 4320 HOUR)) OR
(v.visits_count BETWEEN 11 AND 100 AND websites.last_scanned <= DATE_SUB(NOW(), INTERVAL 2160 HOUR)) OR
(v.visits_count BETWEEN 101 AND 500 AND websites.last_scanned <= DATE_SUB(NOW(), INTERVAL 1080 HOUR)) OR
(v.visits_count BETWEEN 501 AND 1000 AND websites.last_scanned <= DATE_SUB(NOW(), INTERVAL 720 HOUR)) OR
(v.visits_count BETWEEN 1001 AND 2000 AND websites.last_scanned <= DATE_SUB(NOW(), INTERVAL 360 HOUR)) OR
(v.visits_count BETWEEN 2001 AND 5000 AND websites.last_scanned <= DATE_SUB(NOW(), INTERVAL 168 HOUR)) OR
(v.visits_count BETWEEN 5001 AND 10000 AND websites.last_scanned <= DATE_SUB(NOW(), INTERVAL 72 HOUR)) OR
(v.visits_count > 10000 AND websites.last_scanned <= DATE_SUB(NOW(), INTERVAL 24 HOUR));

Answer 3

Just an improvment on #morgb query, using a table for visit count ranges
SQL FIDDLE DEMO
create table visitCount (
`min` bigint(20),
`max` bigint(20),
`frequency` bigint(20)
);
SELECT main.*
FROM (
SELECT
w.web_id,
w.url,
w.last_scanned,
(SELECT COUNT(*)
FROM visits v
WHERE v.web_id = w.web_id
AND TIMESTAMPDIFF(DAY,v.added_on, NOW()) <=30
) AS visit_count,
TIMESTAMPDIFF(HOUR,w.last_scanned, NOW()) AS hrs_since_update
FROM websites w
) main inner join
visitCount v on visit_count between v.min and v.max
WHERE
main.hrs_since_update > v.frequency