Question

I’m trying to come up with a MySQL query to select the last record from each of the previous 7 days. If 1 of the previous 7 days is missing data, I would only get back 6 records. Here’s what I have:

SELECT tracking.* FROM tracking
INNER JOIN 
    (SELECT MAX(lastChecked) AS maxLastChecked, id FROM tracking 
    WHERE lastChecked >= DATE_SUB(lastChecked, INTERVAL 7 DAY ) 
        GROUP BY DAY(lastChecked)) as Lookup ON Lookup.id = tracking.id
            WHERE tracking.propertyID = 1 ORDER BY tracking.lastChecked ASC LIMIT 7

Basically what this should do is select the final recorded entry for propertyID = 1 in the tracking table for each of the past 7 days (starting on today). However, this query is returning this to me (more than ONLY records within the last 7 days):

ID    propertyID  lastChecked              value
2     1           2012-01-25 05:30:00      280
1     1           2012-01-26 12:34:02      268
5     1           2012-01-27 09:51:31      268
83    1           2012-02-13 00:01:07      276

Any help to fix this up would be greatly appreciated!

Answer 1

Try this query:

SELECT tracking.* FROM tracking
INNER JOIN 
    (SELECT MAX(lastChecked) AS maxLastChecked, id FROM tracking 
    WHERE DATEDIFF(lastChecked,NOW())<=7
        GROUP BY DAY(lastChecked)) as Lookup ON Lookup.id = tracking.id
            WHERE tracking.propertyID = 1 ORDER BY tracking.lastChecked ASC