Select hours as columns from Oracle table - sql

Question

I am working with an Oracle database table that is structured like this:
TRANS_DATE TRANS_HOUR_ENDING TRANS_HOUR_SUFFIX READING
1/1/2021 1 1 100
1/1/2021 2 1 105
... ... ... ...
1/1/2021 24 1 115
The TRANS_HOUR_SUFFIX is only used to track hourly readings on days where day light savings time ends (when there could be 2 hours with the same TRANS_HOUR value). This column is the bane of this database's design, however I'm trying to do something to select this data in a certain way. We need a report that columnizes this data based on the hour. Therefore, it would be structured like this (last day shows a day on which DST would end):
TRANS_DATE HOUR_1 HOUR_2_1 HOUR_2_2 ... HOUR_24
1/1/2021 100 105 0 ... 115
1/2/2021 112 108 0 ... 135
... ... ... ... ... ...
11/7/2021 117 108 107 ... 121
I have done something like this before with a PIVOT, however in this case I'm having trouble determining what I should do to account for the suffix. When DST ending happens, we have to account for this hour. I know that we can do this by selecting each hourly value individually with decode or case statements, but that is some messy code. Is there a cleaner way to do this?

Answer 1

You can include multiple source columns in the pivot for() and in() clauses, so you could do:
select *
from (
select trans_date,
trans_hour_ending,
trans_hour_suffix,
reading
from your_table
)
pivot (max(reading) for (trans_hour_ending, trans_hour_suffix)
in ((1, 1) as hour_1, (2, 1) as hour_2_1, (2, 2) as hour_2_2, (3, 1) as hour_3,
-- snip
(23, 1) as hour_23, (24, 1) as hour_24))
order by trans_date;
where every hour has a (24, 1) tuple, and the DST-relevant hour has an extra (2, 2) tuple.
If you don't have rows for every hour - which you don't appear to have form the very brief sample data, at least for suffix 2 for non-DST days - then you will get null results for those, but can replace them with zeros:
select trans_date,
coalesce(hour_1, 0) as hour_1,
coalesce(hour_2_1, 0) as hour_2_1,
coalesce(hour_2_2, 0) as hour_2_2,
coalesce(hour_3, 0) as hour_3,
-- snip
coalesce(hour_23, 0) as hour_23,
coalesce(hour_24, 0) as hour_24
from (
select trans_date,
trans_hour_ending,
trans_hour_suffix,
reading
from your_table
)
pivot (max(reading) for (trans_hour_ending, trans_hour_suffix)
in ((1, 1) as hour_1, (2, 1) as hour_2_1, (2, 2) as hour_2_2, (3, 1) as hour_3,
-- snip
(23, 1) as hour_23, (24, 1) as hour_24))
order by trans_date;
which with slightly expanded sample data gets:
TRANS_DATE HOUR_1 HOUR_2_1 HOUR_2_2 HOUR_3 HOUR_23 HOUR_24
---------- ---------- ---------- ---------- ---------- ---------- ----------
2021-01-01 100 105 0 0 0 115
2021-01-02 112 108 0 0 0 135
2021-11-07 117 108 107 0 0 121
Which is a bit long-winded when you have to include all 25 columns everywhere; but to avoid that you'd have to do a dynamic pivot.

Answer 2

Like I said in my comment, if you can format it with an additional row, I would recommend just having a row for the extra hour. Every other day would look normal. The query to do it would look like this:
CREATE TABLE READINGS
(
TRANS_DATE DATE,
TRANS_HOUR INTEGER,
TRANS_SUFFIX INTEGER,
READING INTEGER
);
INSERT INTO readings
SELECT TO_DATE('01/01/2021', 'MM/DD/YYYY'), 1, 1, 100 FROM DUAL UNION ALL
SELECT TO_DATE('01/01/2021', 'MM/DD/YYYY'), 2, 1, 100 FROM DUAL UNION ALL
SELECT TO_DATE('11/07/2021', 'MM/DD/YYYY'), 1, 1, 200 FROM DUAL UNION ALL
SELECT TO_DATE('11/07/2021', 'MM/DD/YYYY'), 1, 2, 300 FROM DUAL UNION ALL
SELECT TO_DATE('11/07/2021', 'MM/DD/YYYY'), 2, 1, 500 FROM DUAL UNION ALL
SELECT TO_DATE('11/07/2021', 'MM/DD/YYYY'), 2, 2, 350 FROM DUAL;
SELECT TRANS_DATE||DECODE(MAX(TRANS_SUFFIX) OVER (PARTITION BY TRANS_DATE), 1, NULL, 2, ' - '||TRANS_SUFFIX) AS TRANS_DATE,
HOUR_1, HOUR_2, /*...*/ HOUR_24
FROM readings
PIVOT (MAX(READING) FOR TRANS_HOUR IN (1 AS HOUR_1, 2 AS HOUR_2, /*...*/ 24 AS HOUR_24));
This would result in the following results (Sorry, I can't get dbfiddle to work):
TRANS_DATE
HOUR_1
HOUR_2
HOUR_24
01-JAN-21
100
100
-
07-NOV-21 - 1
200
500
-
07-NOV-21 - 2
300
350
-