How to group time column into 5 minute intervals and max/min value respectively SQL?

Question

I have a database with a Datetime column containing intervals of +/- 30 seconds and a Value column containing random numbers between 10 and 100. My table looks like this:

datetime               value
----------------------------
2016-05-04 20:47:20    12
2016-05-04 20:47:40    44
2016-05-04 20:48:30    56
2016-05-04 20:48:40    25
2016-05-04 20:49:30    92
2016-05-04 20:49:40    61
2016-05-04 20:50:00    79
2016-05-04 20:51:20    76
2016-05-04 20:51:30    10
2016-05-04 20:51:40    47
2016-05-04 20:52:40    23
2016-05-04 20:54:00    40
2016-05-04 20:54:10    18
2016-05-04 20:54:50    12
2016-05-04 20:56:00    55

What I want the following output:

datetime               max_val    min_val
-----------------------------------------
2016-05-04 20:45:00    92         12
2016-05-04 20:50:00    79         10
2016-05-04 20:55:00    55         55

Before I can even continue getting the maximum value and the minimum value, I first have to GROUP the datetime column into 5 minute intervals. According to my research I came up with this:

SELECT
  time,
  value
FROM random_number_minute
GROUP BY
  UNIX_TIMESTAMP(time) DIV 300

Which actually GROUPS the datetime column into 5 minute intervals like this:

datetime
-------------------
2016-05-04 20:47:20
2016-05-04 20:50:00
2016-05-04 20:56:00

This comes very close as it takes the next closest datetime to, in this case, 20:45:00, 20:50:00, etc. I would like to rounddown the datetime to the nearest 5 minutes regardless of the seconds, for instance if the minutes are:

minutes    rounddown
--------------------
10         10
11         10
12         10
13         10
14         10
15         15
16         15
17         15
18         15
19         15
20         20

The time could be 14:59 and I would like to rounddown to 10:00. I also tried using this after hours of research:

SELECT
    time,
    time_rounded =
    dateadd(mi,(datepart(mi,dateadd(mi,1,time))/5)*5,dateadd(hh,datediff(hh,0,dateadd(mi,1,time)),0))

But sadly this did not work. I get this error:

Incorrect parameter count in the call to native function 'datediff'

I tried this too:

SELECT  
    time, CASE  
          WHEN  DATEDIFF(second, DATEADD(second, DATEDIFF(second, 0, time_out) / 300 * 300, 0), time) >= 240
            THEN    DATEADD(second, (DATEDIFF(second, 0, time) / 300 * 300) + 300, 0)
            ELSE    DATEADD(second, DATEDIFF(second, 0, time) / 300 * 300, 0)
          END

Returning the same error.

How can I do this? And after the datetime is grouped, how can I get the max and min value of the data grouping?

Answer 1

Sorry if I'm repeating another answer. I'll delete if I am..

SELECT FROM_UNIXTIME(FLOOR(UNIX_TIMESTAMP(datetime)/300)*300) x
     , MIN(value) min_value
     , MAX(value) max_value 
  FROM my_table 
 GROUP 
    BY x;