Oracle PL\SQL to Update Data with the 2nd minimum values between two dates - sql

Question

I have the following problem related industrial pump readings. A pump usually have a meter that keeps the record of volume of material processed by that specific pump. Sometimes the meter needs to be replaced with a entirely new meter (meter reading starts with 0) or an old working meter (meter reading can be more than 0). I have a dataset that keeps maintenance record of the pump with meter readings.
And the indication of a meter change is only when we have data in OLD_METER_READING column, otherwise it is blank.
In ideal scenario the data looks like following:
PUMP_NO INSPECTION_DATE MAINTENANCE_TASK METER_READING OLD_METER_READING TOTAL_PUMP_LIFE
11 11-AUG-2000 A 12489 12489
11 14-JUL-2001 B 14007 14007
11 03-SEP-2002 Y 0 14007 14007
11 03-SEP-2002 C 0 14007 14007
11 03-SEP-2002 B 0 14007 14007
11 04-JUN-2003 A 1200 16007
11 21-DEC-2003 A 8000 22007
11 23-FEB-2004 Y 0 10000 24007
11 26-MAY-2004 B 10 24017
11 26-MAY-2004 P 20 24027
11 26-MAY-2004 R 300 24307
11 04-OCT-2004 B 2312 26319
11 31-MAR-2005 A 2889 26896
11 06-NOv-2006 V 5000 29007
11 14-JUL-2008 T 0 7000 31007
However in many cases the Pump technician will make a mistake in loging METER_READING during change of meter. So the data may end up looking like:
PUMP_NO INSPECTION_DATE MAINTENANCE_TASK METER_READING OLD_METER_READING TOTAL_PUMP_LIFE
11 11-AUG-2000 A 12489 12489
11 14-JUL-2001 B 14007 14007
11 03-SEP-2002 Y 0 14007 14007
11 03-SEP-2002 C 0 14007 14007
11 03-SEP-2002 B 0 14007 14007
11 04-JUN-2003 A 1200 16007
11 21-DEC-2003 A 8000 22007
11 23-FEB-2004 Y 0 10000 24007
11 26-MAY-2004 B 10000 34007
11 26-MAY-2004 P 10000 34007
11 26-MAY-2004 R 10000 34007
11 04-OCT-2004 B 2312 26319
11 31-MAR-2005 A 2889 26896
11 06-NOV-2006 V 5000 29007
11 14-JUL-2008 T 0 7000 31007
The mistake in the 2nd set of data is that the technician rather than loging the actual METER_READING used last METER_READING from old meter as the new METER_READING on the day of 26-MAY-2004. However, correct METER_READING was logged again from 04-OCT-2004. We have numerous occasion where for a specific pump (PUMP_NO) we will have erroneous METER_READING entered in the database after a meter change event. It is also creating wrong and confusing value for the TOTAL_PUMP_LIFE.
So, to correct the data we want to add another column in the table and update the table with a Oracle Procedure where the procedure will check the METER_READING field with the following logic:
check the data between two subsequent meter change event. (for example, in this case between 1st meter 03-SEP-2002 and 2nd meter change-23-FEB-2004. And again between 2nd meter change-23-FEB-2004 and 3rd meter change 14-JUL-2008).
if METER_READING between any of these period is higher at prior date compared to METER_READING on a prior date then update the higher METER_READING with the 2nd lowest value (0 and 2312 are the 2 lowest, so update with 2312) in that period.
So, the period between first 2 meter changes will pass and no update will be necessary.However, in the 2nd set of the date all the values (10000) in the METER_READING column for 26-MAY-2014 will be updated with the value of 2312.
I am not sure how to write a PL\SQL to do the compare the values between two events and also how to update the value of a prior date (if higher value found in the METER_READING column) with a lower value between that period.
Database: Oracle SQL 11g

Answer 1

So in looking at your problem, I don't know that you need to resort to PL/SQL. The following query should help you identify which records are in need of updating:
SELECT m.*,
MIN(meter_reading)
OVER (PARTITION BY m.pump_no
ORDER BY m.inspection_date
RANGE BETWEEN NVL((SELECT min(n.inspection_date)-m.inspection_date
FROM maintenance n
WHERE n.inspection_date > m.inspection_date),
0) FOLLOWING
AND NVL((SELECT min(n.inspection_date)-m.inspection_date-1
FROM maintenance n
WHERE n.old_meter_reading IS NOT NULL
AND n.inspection_date > m.inspection_date),
0) FOLLOWING) AS MIN_READING_FOLLOWING
FROM maintenance m
ORDER BY m.inspection_date, old_meter_reading ASC NULLS LAST;
I created a SQLFiddle to demonstrate the query. (Link)
The analytic MIN function is looking at all rows between the next date a read was performed AND the next meter change to see if any of them have a value which is less than the current read.
You could use this as part of an update statement. As for TOTAL_PUMP_LIFE, it might be easiest to recalculate that after you've corrected the meter_readings as part of a separate operation.
Edit 1: Adding PL/SQL to make updates
DECLARE
CURSOR c_readings IS
SELECT m.*,
MIN(meter_reading)
OVER (PARTITION BY m.pump_no
ORDER BY m.inspection_date
RANGE BETWEEN NVL((SELECT min(n.inspection_date)-m.inspection_date
FROM maintenance n
WHERE n.inspection_date > m.inspection_date),
0) FOLLOWING
AND NVL((SELECT min(n.inspection_date)-m.inspection_date-1
FROM maintenance n
WHERE n.old_meter_reading IS NOT NULL
AND n.inspection_date > m.inspection_date),
0) FOLLOWING) AS MIN_READING_FOLLOWING
FROM maintenance m
ORDER BY m.inspection_date, old_meter_reading ASC NULLS LAST;
BEGIN
FOR rec IN c_readings LOOP
IF rec.meter_reading > rec.min_reading_following THEN
UPDATE maintenance m
SET m.meter_reading = rec.min_reading_following
WHERE m.pump_no = rec.pump_no
AND m.inspection_date = rec.inspection_date
AND m.maintenance_task = rec.maintenance_task;
END IF;
END LOOP;
END;
/
You'll need to either COMMIT when this is done or add it to the code.

Answer 2

Maybe what u need to do is something like this:
update MyTable mt1
set value = (select min(value)
from MyTable2 mt2
where mt1.id = mt2.id --your relation
and value NOT IN (select min(value)
from MyTable2 mt3
where mt2.id = mt3.id))
With this update u are getting the min value and not taking the min value original with the NOT IN.