Question

I am collecting data every five minutes and entering it into a MySQL database. I would like to extract the most recent row that’s over 2 hours old, followed by over 1 hour old, followed by the most recent row.

I was thinking something along the lines of the following, but I think this will get me the last row of each hour. Meaning if I run the query at 8:05 I might get back rows from 6:57, 7:57 and 8:02, the last 2 of which are much less than an hour apart.

SELECT * 
FROM (
    SELECT * 
    FROM mytable 
    ORDER BY Date DESC 
    GROUP BY HOUR(Date) LIMIT 3
) x 
ORDER BY Date ASC

Thanks for any help or suggestions you can provide.

Answer 1

SELECT * FROM (
  SELECT * FROM mytable 
  WHERE `Date`<DATE_SUB(NOW(), INTERVAL 2 HOUR) 
  ORDER BY DATE DESC LIMIT 1
)
UNION
SELECT * FROM (
  SELECT * FROM mytable 
  WHERE `Date`<DATE_SUB(NOW(), INTERVAL 1 HOUR) 
  ORDER BY DATE DESC LIMIT 1
)
UNION
SELECT * FROM (
  SELECT * FROM mytable 
  ORDER BY DATE DESC LIMIT 1
)
ORDER BY `Date`ASC