MySQL count rows within the same intervals to eachother - mysql

Question

I have a table where one column is the date:
+----------+---------------------+
| id | date |
+----------+---------------------+
| 5 | 2012-12-10 10:12:37 |
+----------+---------------------+
| 4 | 2012-12-10 09:09:55 |
+----------+---------------------+
| 3 | 2012-12-09 21:12:35 |
+----------+---------------------+
| 2 | 2012-12-09 20:15:07 |
+----------+---------------------+
| 1 | 2012-12-09 20:01:42 |
+----------+---------------------+
What I need, is to count the rows which are for example whitin 3 hours to each other. In this example I want to join the upper row with the 2nd row, and the 3rd row with the 4th and 5th rows. So my output should be like this:
+----------+---------------------+---------+
| id | date | count |
+----------+---------------------+---------+
| 5 | 2012-12-10 10:12:37 | 2 |
+----------+---------------------+---------+
| 3 | 2012-12-09 21:12:35 | 3 |
+----------+---------------------+---------+
How could I do this?

Answer 1

I think you need a self-join for this:
select t.id, t.date, COUNT(t2.id)
from t left outer join
t t2
on t.date between t2.date - interval 3 hour and t2.date + interval 3 hour
group by t.id, t.date
(This is untested code so it might have a syntax error.)
If you are trying to divide everything into 3-hour intervals, you can do something like:
select max(t.date), t.id, count(*)
from (select t.*,
(date(date)*100 + floor(hour(date)/3)*3) as interval
from t
) t
group by interval

Answer 2

I am not sure how to do this with My SQL but i am able to build a set of queries in SQL Server 2005 which will provide the intended results. Here is the working sample, its very complex and may be overly complex but that's how i was able to get the desired result:
WITH BaseData AS
(
SELECT 5 AS ID, '2012-12-10 10:12:37' AS Date
UNION ALL
SELECT 4 AS ID, '2012-12-10 09:09:55' AS Date
UNION ALL
SELECT 3 AS ID, '2012-12-09 21:12:35' AS Date
UNION ALL
SELECT 2 AS ID, '2012-12-09 20:15:07' AS Date
UNION ALL
SELECT 1 AS ID, '2012-12-09 20:01:42' AS Date
),
BaseDataWithRowNum AS
(
SELECT ID,DATE, ROW_NUMBER() OVER (ORDER BY Date DESC) AS RowNum
FROM BaseData
),
InterRelatedDates AS
(
SELECT B1.RowNum AS RowNum1,B2.RowNum AS RowNum2
FROM BaseDataWithRowNum B1
INNER JOIN BaseDataWithRowNum B2
ON B1.Date BETWEEN B2.Date AND DATEADD(hh,3,B2.Date)
AND B1.RowNum < B2.RowNum
AND B1.ID != B2.ID
),
InterRelatedDatesWithinMultipleGroups AS
(
SELECT G1.RowNum1,G2.RowNum2
FROM InterRelatedDates G1
LEFT JOIN InterRelatedDates G2
ON G1.RowNum2 = G2.RowNum2
AND G1.RowNum1 != G2.RowNum1
)
SELECT BN.ID,
BN.Date,
CountExcludingOriginalGrouppingRecord +1 AS C
FROM
(
SELECT RowNum1 AS RowNum,COUNT(1) AS CountExcludingOriginalGrouppingRecord
FROM
(
-- If a row was used in only one group then it is ok. use as it is
SELECT D1.RowNum1
FROM InterRelatedDatesWithinMultipleGroups AS D1
WHERE D1.RowNum2 IS NULL
UNION ALL
-- In case a row was selected in two groups, choose the one with higher date
SELECT Min(D1.RowNum1)
FROM InterRelatedDatesWithinMultipleGroups AS D1
WHERE D1.RowNum2 IS NOT NULL
GROUP BY D1.RowNum2
) T
GROUP BY RowNum1
) T2
INNER JOIN BaseDataWithRowNum BN
ON BN.RowNum = T2.RowNum