Oracle query to check for failure more than 90 % - sql

Question

I have a situation where I need to write a monitoring query to run every 2 hour to raise alert when processed count becomes less than 90%.
Lets say we have a Table Incoming Message where all incoming messages are captured and another table where all processed messages are captured.
This is what I came up with, this works but I am wondering if there is better way of doing this?
SELECT (CASE WHEN PROCESSEDCOUNT <= INCOMINGCOUNT * .9
THEN 'ALERT:: Process Count ' || PROCESSEDCOUNT || ' is less than 90% of Incoming count ' || INCOMINGCOUNT || '. '
ELSE 'FINE:: Process Count ' || PROCESSEDCOUNT || ' is more than or equal to 90% of Incoming count ' || INCOMINGCOUNT || '. '
END ) as Status
from
(SELECT
(SELECT COUNT(*)
FROM INCOMING_TABLE D WHERE INSERTION_TIME > SYSDATE - (1/12)
AND EXISTS (SELECT * FROM PROCESSED_TABLE C WHERE ( D.MESSAGE_ID = C.MESSAGE_ID)
AND C.PROCESSED_TIME > SYSDATE- (1/12))) AS PROCESSEDCOUNT,
(SELECT COUNT(*) FROM INCOMING_TABLE WHERE INSERTION_TIME > SYSDATE - (1/12)) AS INCOMINGCOUNT
FROM DUAL);
PROCESSED_TABLE used for storing other records as well, that is the
reason I need to use EXISTS to figure out process count.
I understand as time captured in two tables may not fall into same
time duration. We are not worried about that right now, just want to
make sure majority of records processed.
We are using oracle 11g, if that helps.

Answer 1

You are querying the same data from INCOMING_TABLE twice, which isn't really efficient ;-)
One possibility could be to outer join:
SELECT
CASE
WHEN COUNT(C.MESSAGE_ID) <= COUNT(*) * .9
THEN 'ALERT:: Process Count ' || COUNT(C.MESSAGE_ID) || ' is less than 90% of Incoming count ' || COUNT(*) || '. '
ELSE 'FINE:: Process Count ' || COUNT(C.MESSAGE_ID) || ' is more than or equal to 90% of Incoming count ' || COUNT(*) || '. '
END as Status
FROM INCOMING_TABLE D
LEFT OUTER JOIN PROCESSED_TABLE C
ON C.MESSAGE_ID = D.MESSAGE_ID
AND C.PROCESSED_TIME > SYSDATE- (1/12)
WHERE D.INSERTION_TIME > SYSDATE - (1/12)
/
That will work if you can be sure either zero or one record exists in PROCESSED_TABLE for each message_id. Maybe you can add a AND C.PROCESS_TYPE = ... or something to make that condition come true.
If you cannot guarantee that a join to PROCESSED_TABLE returns at most one row, you can move your EXISTS to inside a COUNT instead of the WHERE clause and thereby again avoid accessing INCOMING_TABLE twice:
SELECT (CASE WHEN PROCESSEDCOUNT <= INCOMINGCOUNT * .9
THEN 'ALERT:: Process Count ' || PROCESSEDCOUNT || ' is less than 90% of Incoming count ' || INCOMINGCOUNT || '. '
ELSE 'FINE:: Process Count ' || PROCESSEDCOUNT || ' is more than or equal to 90% of Incoming count ' || INCOMINGCOUNT || '. '
END ) as Status
from
(
SELECT COUNT(*) INCOMINGCOUNT
, COUNT(
CASE
WHEN EXISTS (SELECT * FROM PROCESSED_TABLE C
WHERE D.MESSAGE_ID = C.MESSAGE_ID
AND C.PROCESSED_TIME > SYSDATE- (1/12))
THEN 1
END
) PROCESSEDCOUNT
FROM INCOMING_TABLE D
WHERE D.INSERTION_TIME > SYSDATE - (1/12)
)
/
(PS. If you are at the start of writing a lot of code to handle a messaging queue, I would also suggest like #DARK_A to look into Advanced Queues instead of building your own. There is a lot of issues you need to handle in a messaging system, so why have that trouble if you can use what Oracle has already built ;-)