To find the last value in the dataset of 15 minutes interval - mysql

Question

ID Timestamp Value
1 11:59.54 10
1 12.04.00 20
1 12.12.00 31
1 12.16.00 10
1 12.48.00 05
I want the result set as
ID Timestamp Value
1 11:59.54 10
1 12:00:00 10
1 12.04.00 20
1 12.12.00 31
1 12:15:00 31
1 12:16.00 10
1 12:30:00 10
1 12:45:00 10
1 12.48.00 05

Answer 1

More coffee will probably lead to a simpler solution, but consider the the following...
DROP TABLE IF EXISTS my_table;
CREATE TABLE my_table
(id INT NOT NULL AUTO_INCREMENT PRIMARY KEY
,timestamp TIMESTAMP
,value INT NOT NULL
);
INSERT INTO my_table VALUES
(1 ,'11:59:54',10),
(2 ,'12:04:00',20),
(3 ,'12:12:00',31),
(4 ,'12:16:00',10),
(5 ,'12:48:00',05);
... in addition, I have a table of integers, that looks like this:
SELECT * FROM ints;
+---+
| i |
+---+
| 0 |
| 1 |
| 2 |
| 3 |
| 4 |
| 5 |
| 6 |
| 7 |
| 8 |
| 9 |
+---+
So...
SELECT a.timestamp
, b.value
FROM
( SELECT x.*
, MIN(y.timestamp) min_timestamp
FROM
( SELECT timestamp
FROM my_table
UNION
SELECT SEC_TO_TIME((i2.i*10+i1.i)*900)
FROM ints i1
, ints i2
WHERE SEC_TO_TIME((i2.i*10+i1.i)*900)
BETWEEN (SELECT MIN(timestamp) FROM my_table)
AND (SELECT MAX(timestamp) FROM my_table)
ORDER
BY timestamp
) x
LEFT
JOIN my_table y
ON y.timestamp >= x.timestamp
GROUP
BY x.timestamp
) a
JOIN my_table b
ON b.timestamp = min_timestamp;
+-----------+-------+
| timestamp | value |
+-----------+-------+
| 11:59:54 | 10 |
| 12:00:00 | 20 |
| 12:04:00 | 20 |
| 12:12:00 | 31 |
| 12:15:00 | 10 |
| 12:16:00 | 10 |
| 12:30:00 | 5 |
| 12:45:00 | 5 |
| 12:48:00 | 5 |
+-----------+-------+

Answer 2

The idea is as follows. Use SERIES_GENERATE() to generate the missing time stamps with the 15 minute intervals and and union it with the existing data your table T. Now you would want to use LAST_VALUE with IGNORE NULLS. IGNORE NULLS is not implemented in HANA, therefore you have to do a bit of a workaround. I use COUNT() as a window function to count the non null values. I do the same on the original data and then join both on the count. This way I repeat the last non-null value.
select X.ID, X.TIME, Y.VALUE from (
select ID, TIME, value,
count(VALUE) over (order by TIME rows between unbounded preceding and current row) as CNT
from (
--add the missing 15 minute interval timestamps
select 1 as ID, GENERATED_PERIOD_START as TIME, NULL as VALUE
from SERIES_GENERATE_TIME('INTERVAL 15 MINUTE', '12:00:00', '13:00:00')
union all
select ID, TIME, VALUE from T
)
) as X join (
select ID, TIME, value,
count(value) over (order by TIME rows between unbounded preceding and current row) as CNT
from T
) as Y on X.CNT = Y.CNT