Teradata sql query from grouping records using Intervals - sql

Question

In Teradata SQL how to assign same row numbers for the group of records created with in 8 seconds of time Interval.
Example:-
Customerid Customername Itembought dateandtime
(yyy-mm-dd hh:mm:ss)
100 ALex Basketball 2017-02-10 10:10:01
100 ALex Circketball 2017-02-10 10:10:06
100 ALex Baseball 2017-02-10 10:10:08
100 ALex volleyball 2017-02-10 10:11:01
100 ALex footbball 2017-02-10 10:11:05
100 ALex ringball 2017-02-10 10:11:08
100 Alex football 2017-02-10 10:12:10
My Expected result shoud have additional column with Row_number where it should assign the same number for all the purchases of the customer with in 8 seconds: Refer the below expected result
Customerid Customername Itembought dateandtime Row_number
(yyy-mm-dd hh:mm:ss)
100 ALex Basketball 2017-02-10 10:10:01 1
100 ALex Circketball 2017-02-10 10:10:06 1
100 ALex Baseball 2017-02-10 10:10:08 1
100 ALex volleyball 2017-02-10 10:11:01 2
100 ALex footbball 2017-02-10 10:11:05 2
100 ALex ringball 2017-02-10 10:11:08 2
100 Alex football 2017-02-10 10:12:10 3

Answer 1

This is one way to do it with a recursive cte. Reset the running total of difference from the previous row's timestamp when it gets > 8 to 0 and start a new group.
WITH ROWNUMS AS
(SELECT T.*
,ROW_NUMBER() OVER(PARTITION BY ID ORDER BY TM) AS RNUM
/*Replace DATEDIFF with Teradata specific function*/
,DATEDIFF(SECOND,COALESCE(MIN(TM) OVER(PARTITION BY ID
ORDER BY TM ROWS BETWEEN 1 PRECEDING AND CURRENT ROW), TM),TM) AS DIFF
FROM T --replace this with your tablename and add columns as required
)
,RECURSIVE CTE(ID,TM,DIFF,SUM_DIFF,RNUM,GRP) AS
(SELECT ID,
TM,
DIFF,
DIFF,
RNUM,
CAST(1 AS int)
FROM ROWNUMS
WHERE RNUM=1
UNION ALL
SELECT T.ID,
T.TM,
T.DIFF,
CASE WHEN C.SUM_DIFF+T.DIFF > 8 THEN 0 ELSE C.SUM_DIFF+T.DIFF END,
T.RNUM,
CAST(CASE WHEN C.SUM_DIFF+T.DIFF > 8 THEN T.RNUM ELSE C.GRP END AS int)
FROM CTE C
JOIN ROWNUMS T ON T.RNUM=C.RNUM+1 AND T.ID=C.ID
)
SELECT ID,
TM,
DENSE_RANK() OVER(PARTITION BY ID ORDER BY GRP) AS row_num
FROM CTE
Demo in SQL Server

Answer 2

I am going to interpret the problem differently from vkp. Any row within 8 seconds of another row should be in the same group. Such values can chain together, so the overall span can be more than 8 seconds.
The advantage of this method is that recursive CTEs are not needed, so it should be faster. (Of course, this is not an advantage if the OP does not agree with the definition.)
The basic idea is to look at the previous date/time value; if it is more than 8 seconds away, then add a flag. The cumulative sum of the flag is the row number you are looking for.
select t.*,
sum(case when prev_dt >= dateandtime - interval '8' second
then 0 else 1
end) over (partition by customerid order by dateandtime
) as row_number
from (select t.*,
max(dateandtime) over (partition by customerid order by dateandtime row between 1 preceding and 1 preceding) as prev_dt
from t
) t;

Answer 3

Using Teradata's PERIOD data type and the awesome td_normalize_overlap_meet:
Consider table test32:
SELECT * FROM test32
+----+----+------------------------+
| f1 | f2 | f3 |
+----+----+------------------------+
| 1 | 2 | 2017-05-11 03:59:00 PM |
| 1 | 3 | 2017-05-11 03:59:01 PM |
| 1 | 4 | 2017-05-11 03:58:58 PM |
| 1 | 5 | 2017-05-11 03:59:26 PM |
| 1 | 2 | 2017-05-11 03:59:28 PM |
| 1 | 2 | 2017-05-11 03:59:46 PM |
+----+----+------------------------+
The following will group your records:
WITH
normalizedCTE AS
(
SELECT *
FROM TABLE
(
td_normalize_overlap_meet(NEW VARIANT_TYPE(periodCTE.f1), periodCTE.fper)
RETURNS (f1 integer, fper PERIOD(TIMESTAMP(0)), recordCount integer)
HASH BY f1
LOCAL ORDER BY f1, fper
) as output(f1, fper, recordcount)
),
periodCTE AS
(
SELECT f1, f2, f3, PERIOD(f3, f3 + INTERVAL '9' SECOND) as fper FROM test32
)
SELECT t2.f1, t2.f2, t2.f3, t1.fper, DENSE_RANK() OVER (PARTITION BY t2.f1 ORDER BY t1.fper) as fgroup
FROM normalizedCTE t1
INNER JOIN periodCTE t2 ON
t1.fper P_INTERSECT t2.fper IS NOT NULL
Results:
+----+----+------------------------+-------------+
| f1 | f2 | f3 | fgroup |
+----+----+------------------------+-------------+
| 1 | 2 | 2017-05-11 03:59:00 PM | 1 |
| 1 | 3 | 2017-05-11 03:59:01 PM | 1 |
| 1 | 4 | 2017-05-11 03:58:58 PM | 1 |
| 1 | 5 | 2017-05-11 03:59:26 PM | 2 |
| 1 | 2 | 2017-05-11 03:59:28 PM | 2 |
| 1 | 2 | 2017-05-11 03:59:46 PM | 3 |
+----+----+------------------------+-------------+
A Period in Teradata is a special data type that holds a date or datetime range. The first parameter is the start of the range and the second is the ending time (up to, but not including which is why it's "+ 9 seconds"). The result is that we get a 8 second time "Period" where each record might "intersect" with another record.
We then use td_normalize_overlap_meet to merge records that intersect, sharing the f1 field's value as the key. In your case that would be customerid. The result is three records for this one customer since we have three groups that "overlap" or "meet" each other's time periods.
We then join the td_normalize_overlap_meet output with the output from when we determined the periods. We use the P_INTERSECT function to see which periods from the normalized CTE INTERSECT with the periods from the initial Period CTE. From the result of that P_INTERSECT join we grab the values we need from each CTE.
Lastly, Dense_Rank() gives us a rank based on the normalized period for each group.