Record events if values have changed in the last 3 days

问题

I have a question, I have a table of importance. But the difference between these values is 3 days.

select 
    er.name,
    er.temp as real_temp, 
    der.temp as old_temp
from TEMPR_SILO er
    left join TEMPR_SILO der
    on er.name = der.name
where der.ID_TRANS in (select max(ID_TRANS) - 72 from TEMPR_SILO) 
    and er.ID_TRANS  in (select max(ID_TRANS) from TEMPR_SILO)

My answer

NAME	      REAL_TEMP	OLD_TEMP
SENSOR0001	7.98	    9.66
SENSOR0002	8.04	    9.91
SENSOR0003	7.91	    0.41
SENSOR0004	9.54	   -0.27
SENSOR0005	9.85	   -1.09
SENSOR0006	9.35	   -1.59
SENSOR0007	8.54	   -1.34

That is, in the answer I have the name of the sensor, and the temperature is real and old which is already 3 days. I have a question, can I make it so that if the temperature drops to 5, then I have a spare ALARM table that

 INSERT INTO ALARM ( NAME, INFO)    VALUES ( er.name ,'The temperature has greatly changed')

The table will have 600 values always. Thanks for the help) I want to implement this code in a background task that will be called every hour)

回答1:

You may add following query in your background task that will serve the purpose.

INSERT INTO IMS.ALARM (NAME,INFO)  
select er.name,'The temperature has significantly dropped'
from IMS.TEMPR_SILO er
    left join IMS.TEMPR_SILO der on er.name = der.name
where der.ID_TRANS in (select max(ID_TRANS) - 72 from IMS.TEMPR_SILO) 
and er.ID_TRANS  in (select max(ID_TRANS) from IMS.TEMPR_SILO)
and der.temp-er.temp>=6;

In my opinion, your solution can be little improved if you manage Alarming stuff in Trigger instead of some background process because there are some drawbacks in this way e.g.

Continuous background process will be doing hourly extra DB I/O in addition to consuming processing power
For any given reasons, if new records are not coming then program may register/insert new alarms on the basis of obsolete data

However, if you write a trigger 'ON INSERT' event on same table TEMPR_SILO by using above mentioned query then:

It will be executed automatically as and when new record gets inserted
False Alarms can be avoided
No background process will be required

I hope this solution will work for you.

来源：https://stackoverflow.com/questions/60503335/record-events-if-values-have-changed-in-the-last-3-days

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sql

Oracle

oracle11g