Question

I have a database table like this:

id     date                     value    minute
1      20100201 00:00:01.909    xxx      0   
2      20100201 00:00:02.408    xxx      0
3      20100201 00:01:02.412    xxx      1 
4      20100201 00:01:02.909    xxx      1 
5      20100201 00:01:02.921    xxx      1   
6      20100201 00:01:02.955    xxx      1
7      20100201 00:02:01.903    xxx      2
8      20100201 00:02:25.332    xxx      2
9      20100201 00:03:12.003    xxx      3
10     20100201 00:04:12.003    xxx      4

…

I want the results to be:

id    date                      value1   minute
1      20100201 00:00:01.909    xxx      0   
2      20100201 00:00:02.408    xxx      0
3      20100201 00:01:02.412    xxx      1
6      20100201 00:01:02.955    xxx      1
7      20100201 00:02:01.903    xxx      2
8      20100201 00:02:25.332    xxx      2
9      20100201 00:03:12.003    xxx      3

I want to query it and return the id with the first & last number for each minute and 1 record per minute if only 1 exists (so id 1,2,3,6,7,8,9 in the above).

I’ve tried using group by ordering by id ASC – group by minute but it seems to order after its grouped, so this doesn’t work.

Anyone got any ideas? I can’t believe it can’t be done!

Answer 1

Try this query –

SELECT t1.* FROM test_table t1
  JOIN (
    SELECT MIN(id) min_id, MAX(id) max_id FROM test_table
      GROUP BY TIME_TO_SEC(TIME(date)) DIV 60) t2
  ON t1.id = t2.min_id OR t1.id = t2.max_id

If date field is not a DATETIME or TIMESTAMP, then GROUP BY should be modified.
Also, I advise you to group by exact minute (e.g. – group by year, day_of_year, minute_of_day).