Can "NOT EXISTS" replace "NOT IN" by only swapping the sentences? - db2

Question

How would I make NOT EXISTS work here when it works correctly with NOT IN and I should be getting the same results using NOT EXISTS but I am not.
What is wrong with my logic in using the NOT EXISTS sentence
The NOT EXISTS should be comparing to A.C_SEQUENCE like the NOT IN. Same logic as the NOT IN which gives me the correct records.
Select A.C_SEQUENCE, A.STATUS
FROM PROD.CONTROL A
where A.AID = 'BILLINGS'
and A.USER='GLOBAL_NETWORK'
--and A.STATUS = 'ON'
and NOT EXISTS
(
select B.H_SEQUENCE
from PROD.STATUS_R B, PROD.CONTROL A
where A.USER='GLOBALNETWORK'
and A.C_SEQUENCE = B.H_SEQUENCE
and B.H_STAT in('IGN','ACK')
)
order by C_date DESC limit 5000
Select A.C_SEQUENCE, A.STATUS
FROM PROD.CONTROL A
where A.AID = 'BILLINGS'
and A.USER='GLOBAL_NETWORK'
--and A.STATUS = 'ON'
and A.C_SEQUENCE NOT IN
(
select B.H_SEQUENCE
from PROD.STATUS_R B, PROD.CONTROL A
where A.USER='GLOBALNETWORK'
and A.C_SEQUENCE = B.H_SEQUENCE
and B.H_STAT in('IGN','ACK')
)
order by C_date DESC limit 5000

Answer 1

Without sample data, this is just a shot in the dark, but I would write the NOT EXISTS version this way:
Select A.C_SEQUENCE, A.STATUS
FROM PROD.CONTROL A
where A.AID = 'BILLINGS'
and A.USER='GLOBAL_NETWORK'
--and A.STATUS = 'ON'
and NOT EXISTS
(
select *
from PROD.STATUS_R B
and A.C_SEQUENCE = B.H_SEQUENCE
and B.H_STAT in('IGN','ACK')
)
order by C_date DESC limit 5000
NOT EXISTS means that you only want outer select records where the sub-select does not return a record. But really, since the sub-select does not include much that is not already in the outer select, It might perform better to write this thing like this:
Select A.C_SEQUENCE, A.STATUS
FROM PROD.CONTROL A
left exception join prod.status_r_b b
on b.h_sequence = a.c_sequence
and b.h_stat in ('IGN', 'ACK')
where A.AID = 'BILLINGS'
and A.USER='GLOBAL_NETWORK'
--and A.STATUS = 'ON'
order by C_date DESC limit 5000
You should also be able to simplify the NOT IN version like this:
Select A.C_SEQUENCE, A.STATUS
FROM PROD.CONTROL A
where A.AID = 'BILLINGS'
and A.USER='GLOBAL_NETWORK'
--and A.STATUS = 'ON'
and A.C_SEQUENCE NOT IN
(
select B.H_SEQUENCE
from PROD.STATUS_R B
and B.H_STAT in('IGN','ACK')
)
order by C_date DESC limit 5000
In this case NOT IN acknowledges that rows could be returned, but you are only going to select rows from prod.control where the sequence number is not in the filtered prod.status_r result set.