Aggregating MySQL data on hourly basis from minute-wise raw data

问题

I have a table, table_1, which has data for EACH minute and looks like:

+---------------------+---------+
| date_time           | value   |
+---------------------+---------+
| 2015-06-05 18:00:00 | 222.663 |
| 2015-06-05 18:01:00 | 222.749 |
| 2015-06-05 18:02:00 | 222.957 |
| 2015-06-05 18:03:00 | 223.063 |
| 2015-06-05 18:04:00 | 223.117 |
+---------------------+---------+

I wish to fetch hourly min and max values. Something like:

+---------------------+---------+
| date_time           | value   |
+---------------------+---------+
| 2015-06-05 18:10:00 | 200.663 |
| 2015-06-05 18:45:00 | 222.749 |
| 2015-06-05 19:10:00 | 190.957 |
| 2015-06-05 19:33:00 | 400.063 |
+---------------------+---------+

Currently I am creating a for loop in PHP and runs a query for EACH hour. However, it is obviously not the best way to do it, and is thus VERY TIME CONSUMING. For example:

for($temp = $st; $temp <= $et; $temp = $temp + 60){//looping for each hour

 $sql1 = "select * from table_1 where value in 
 (select max(value) from table_1 
 where date_time >= '".date('Y-m-d H:i:s',$st)."' 
 and date_time < '".date('Y-m-d H:i:s',$temp)."' ) 
 and date_time >= '".date('Y-m-d H:i:s',$st)."' 
 and date_time < '".date('Y-m-d H:i:s',$temp)."' limit 1";

 $rs1 = mysql_query($sql1);

 $row1 = mysql_fetch_assoc($rs1)
 $val1 = $row1['value']; 
 $date1 = $row1['date_time'];

}

回答1:

Anawer for the question

select DATE_FORMAT(date_time,'%Y-%m-%d %H:00:00') h, min(value), max(value)
    from thetable 
  group by h

1. How to do the same thing for intervals like 6 hours or 15 minutes.

for 15 minute interval:

select date_time, min(value), max(value) 
     from t1 
  group by round(unix_timestamp(date_time)/(15 * 60))

For 6 hours interval change to (6 * 60 * 60)

2. The result above does NOT show the original time stamp corresponding to the min and max values. How to get those.

Such query give you what you want. But if, for example, there are some minimum values in an interval, get so many rows how many such values

select date_time, value 
    from t1, 
         (select DATE_FORMAT(date_time,'%Y-%m-%d %H:00:00') h, 
                 min(value) min, max(value) max 
              from t1 
            group by h
         ) t 
  where value in (min, max) 
    and DATE_FORMAT(date_time,'%Y-%m-%d %H:00:00') = h

来源：https://stackoverflow.com/questions/32421110/aggregating-mysql-data-on-hourly-basis-from-minute-wise-raw-data

标签

mysql

group-by

aggregate-functions