MySQL选择按日期顺序排序然后按列分组

Question

Hi i want to select from a table order by date desc than gruoup by smth. At first phpmyadmin give an error (sql_mode=only_full_group_by) and i fix it by removing that flag from my.cnf and i don't know if this fix is good for long term, i read somewhere that with this fix you can get unwanted results. i've tried **select * from ( select * from log order by date desc) tmp group by imei** but the results are from the oldest date not from the newest date, it gives me the imei from the first id not from the last.

Answer 1

For the grouping result, it doesn't matter if you've ordered the input. If I interpret your question correctly, you want to get the latest log entry for each imei. You would have to do something like this:

SELECT l1.*
  FROM logs as l1
  LEFT OUTER JOIN logs as l2
  ON l1.imei = l2.imei
    AND l1.date < l2.date
  WHERE l2.date IS NULL

where you are essentially asking for each log entry (l1) for which no log entry (l2) exists with the same imei, but a greater date.

If you only want to know when the last log entry for each imei was, this will be enough:

SELECT imei, MAX(date)
  FROM log
  GROUP BY imei

Answer 2

SELECT * FROM日志WHERE ID in（imei的SELECT max（id）FROM日志组）