SQL query where clause for reporting - sql

Question

Let's say I have this table with the following data:
Service_ID Cust_ID Service_Date Next_Service_Date
-----------------------------------------------------
1 15 2016-01-1 2016-01-31
2 21 2016-01-1 2016-01-31
3 15 2016-01-31 2016-03-1
I need a condition to check if Next_Service_Date is found in Service_Date for each customer not the whole table.
For example customer with id = 15 and Service_ID = 3, you can see Service_Date was made on 2016-01-31
Same as the Next_Service_Date with Service_ID = 1
So output of the query should be
Service_ID Cust_ID Service_Date Next_Service_Date
------------------------------------------------------
2 21 2016-01-1 2016-01-31
I hope I made everything clear.
Note why I want to show record # 2 because that customer has no records in Service_Date that matches the date in Next_Service_Date

Answer 1

If I understand correctly, you want not exists:
select bt.*
from belowtable bt
where not exists (select 1
from belowtable bt2
where bt2.cust_id = bt.cust_id and
(bt2.next_service_date = bt.service_date or
bt2.service_date = bt.next_serice_date
)
);

Answer 2

Edited -- I think I understand your question now -- you want to find all records that should have a next service date scheduled but do not? If so, a combination semi-join and anti-join would do it.
If I'm off the mark, please let me know where I misunderstood.
select
t1.*
from
MyTable t1
where exists (
select null
from MyTable t2
where
t1.Next_Service_Date = t2.Service_Date
)
and not exists (
select null
from MyTable t2
where
t1.Cust_Id = t2.Cust_Id and
t1.Next_Service_Date = t2.Service_Date
)