Calculate the time difference and the calculation between of two rows

Question

I have a table with a specified id, valued, validate and value

MyTable looks like this:

+------+------------+---------------------+-------+
| ID   | VALUEID    | VALUEDATE           | VALUE |
+------+------------+---------------------+-------+
| 1    | 2          | 2015-12-21 16:30:00 | 50    |
| 2    | 1          | 2015-12-22 16:33:00 | 54    |
| 3    | 8          | 2015-12-23 16:54:00 | 58    |
| 4    | 6          | 2015-12-24 17:11:00 | 62    |
| 5    | 8          | 2015-12-25 17:11:00 | 66    |
| 6    | 10         | 2015-12-26 10:01:00 | 70    |
| 7    | 7          | 2015-12-27 11:00:00 | 74    |
| 8    | 9          | 2015-12-28 12:03:00 | 78    |
| 9    | 7          | 2015-12-29 12:05:00 | 82    |
| 10   | 6          | 2015-12-30 12:05:00 | 86    |
| 11   | 3          | 2016-01-01 13:19:00 | 90    |
| 12   | 2          | 2016-01-02 13:20:00 | 94    |
| 13   | 7          | 2016-01-03 13:21:00 | 98    |
| 14   | 6          | 2016-01-04 13:51:00 | 102   |
| 15   | 9          | 2016-01-05 13:53:00 | 106   |
| 16   | 3          | 2016-01-06 14:51:00 | 110   |
| 17   | 6          | 2016-01-07 15:31:00 | 114   |
| 18   | 10         | 2016-01-08 15:32:00 | 118   |
| 19   | 7          | 2016-01-09 15:33:00 | 122   |
| 20   | 6          | 2016-01-10 15:34:00 | 126   |
+------+------------+---------------------+-------+

When I want the result, which valueid = 6. I am using the this code.

SELECT id, valueid, valuedate, value FROM MyTable WHERE valueid =6

The result looks like this.

+------+------------+---------------------+-------+
| ID   | VALUEID    | VALUEDATE           | VALUE |
+------+------------+---------------------+-------+
| 4    | 6          | 2015-12-24 17:11:00 | 62    |
| 10   | 6          | 2015-12-30 12:05:00 | 86    |
| 14   | 6          | 2016-01-04 13:51:00 | 102   |
| 17   | 6          | 2016-01-07 15:31:00 | 114   |
| 20   | 6          | 2016-01-10 15:34:00 | 126   |
+------+------------+---------------------+-------+

But I want to calculate the results.

I'd like to count how many days the previous entry is. Also, a small calculation should be calculated. B-value (minus) A value (divide) days.

I tried something like this, but I did not get the result.

SELECT A.id, A.valueid, A.valuedate, A.value, (B.valuedate - A.valuedate) AS valuedatediff, (B.value - A.value / valuedatediff) AS valuecalc FROM MyTable A INNER JOIN MyTable B ON B.valueid = (A.valueid + 1) WHERE A.valueid =6

Anyway, I would like this result.

+------+------------+---------------------+-------+---------------+-----------+
| ID   | VALUEID    | VALUEDATE           | VALUE | VALUEDATEDIFF | VALUECALC |
+------+------------+---------------------+-------+---------------+-----------+
| 4    | 6          | 2015-12-24 17:11:00 | 62    | 5             | 4.8       |
| 10   | 6          | 2015-12-30 12:05:00 | 86    | 5             | 3.2       |
| 14   | 6          | 2016-01-04 13:51:00 | 102   | 3             | 4         |
| 17   | 6          | 2016-01-07 15:31:00 | 114   | 3             | 4         |
| 20   | 6          | 2016-01-10 15:34:00 | 126   | 0             | 0         |
+------+------------+---------------------+-------+---------------+-----------+

Thanks!

Answer 1

A little fix to output.

SELECT a.id
     , a.valueid
     , a.valuedate
     , a.value
     , a.value - b.value valuediff
     , DATEDIFF(a.valuedate,b.valuedate) AS valuedatediff
     , (a.value - b.value)/(DATEDIFF(a.valuedate,b.valuedate)) AS valuecalc
  FROM 
     ( SELECT x.*
            , MAX(y.id) max_id
         FROM my_table x 
         LEFT 
         JOIN my_table y 
           ON y.valueid = x.valueid 
          AND y.id < x.id 
        WHERE x.valueid = 6
        GROUP 
           BY x.id
     ) a
  LEFT
  JOIN my_table b
    ON b.id = a.max_id
ORDER BY a.valuedate DESC 

And now, the latest date first.

+------+------------+---------------------+-------+-----------+---------------+-----------+
| ID   | VALUEID    | VALUEDATE           | VALUE | VALUEDIFF | VALUEDATEDIFF | VALUECALC |
+------+------------+---------------------+-------+-----------+---------------+-----------+
| 20   | 6          | 2016-01-09 15:34:00 | 126   | 12        | 3             | 4         |
| 17   | 6          | 2016-01-06 15:31:00 | 114   | 12        | 3             | 4         |
| 14   | 6          | 2016-01-03 13:51:00 | 102   | 16        | 4             | 4         |
| 10   | 6          | 2015-12-30 12:05:00 | 86    | 24        | 6             | 4         |
| 4    | 6          | 2015-12-24 17:11:00 | 62    | NULL      | NULL          | NULL      |
+------+------------+---------------------+-------+-----------+---------------+-----------+

Hopefully, this is right :)

Answer 2

E.g.:

SELECT a.id
     , a.valueid
     , a.valuedate
     , a.value
     , b.value - a.value valuediff
     , COALESCE(DATEDIFF(b.valuedate,a.valuedate),0) valuedatediff
     , COALESCE((b.value - a.value)/(DATEDIFF(b.valuedate,a.valuedate)),0) valuecalc
  FROM 
     ( SELECT x.*
            , MIN(y.id) min_id
         FROM my_table x 
         LEFT 
         JOIN my_table y 
           ON y.valueid = x.valueid 
          AND y.id > x.id 
        WHERE x.valueid = 6 
        GROUP 
           BY x.id
     ) a
  LEFT
  JOIN my_table b
    ON b.id = a.min_id;