How to write Oracle Sql Query combining multiple tables

Question

I have 4 tables called A, B, C, C_History. Below is what is each table contains. cust_id is the common identifier for all tables.

A - cust_id,status,cust_type

B - cust_id,acnt_nmbr,acnt_systm

C - cust_id,email,mod_date

C_History - cust_id,email,mod_date(Same as C, used to insert rows which were deleted/updated in C).

I need to write a query combing all above tables to pull A.cust_id, B.acnt_nmbr,C.email(As New Email),C_History(As Old Email).

Caveat here is that, A and B tables will have only one record for a cust_id, but C and C_History can have multiple email records for a cust_id.

So from C table, i just need single email which was latest by using mod_date (TIMESTAMP datatype),

And from C_Hisory also, i just need single latest email using mod_date, but one more condition is that, whichever latest email picked from C_History, should not be same as the latest email picked from C.

Please help with this as i am banging my head from 2 days trying to figure this out.

Thank you legends in Advance.

Answer 1

SELECT A.cust_id
    ,B.acnt_nmbr
    ,C.email
    ,C_History.email
FROM A
    ,B
    ,(
        SELECT cust_id
            ,MAX(email) KEEP (
                DENSE_RANK LAST ORDER BY mod_date
                ) OVER (PARTITION BY cust_id)
        FROM c
        ) c
    ,(
        SELECT cust_id
            ,MAX(email) KEEP (
                DENSE_RANK LAST ORDER BY mod_date
                ) OVER (PARTITION BY cust_id)
        FROM c_history
        ) c_history
WHERE a.cust_id = b.cust_id
    AND c_history.cust_id = a.cust_id
    AND c.cust_id = a.cust_id