Can INNER JOIN replace a column's value with another value from the same table - for all rows

Question

I need to write a query to replace one of the column's values with a value from another row in the same table. I tried to use a simple inner join, but I'm not seeing the results I need.

Here's an example of the table BANK_LOANS:

MONTH_ID   LOAN_NUMBER    BANK_NAME       AMOUNT
========   ===========    ==========      ========
76         00-100         Bank One        100.00
75         00-100         The Bank One    150.00
74         00-100         Bank 1          150.00
76         00-200         Another Bank    300.00 
75         00-200         Another Bank    500.00

The data is loaded from outside sources which doesn't verify the bank name, so the spelling for a bank name for a given loan number can possibly vary. The customer wants whatever BANK_NAME is in the database for the max MONTH_ID to be used for all the results for that LOAN_NUMBER, and they want the results sorted by BANK_NAME. So for instance, loan 00-100 needs a BANK_NAME of "Bank One" for all rows.

I tried using an inner join to do this, but wasn't getting the correct results

SELECT name.BANK_NAME, 
       bl.LOAN_NUMBER,
       bl.AMOUNT
FROM BANK_LOANS    
INNER JOIN BANK_LOANS home
    ON name.LOAN_NUMBER = bl.LOAN_NUMBER
    AND name.MONTH_ID = 67  --the max id provided to the query
ORDER BY name.BANK_NAME, bl.LOAN_NUMBER, bl.MONTH_ID DESC

I think I have it working with an sub-query, but it's kind of ugly. I was wondering if there was a better way (best practices) of accomplishing this with joins or other oracle functions.

This seems to work, but it just feels wrong:

SELECT name.BANK_NAME, 
       bl.LOAN_NUMBER,
       bl.AMOUNT
FROM BANK_LOANS, 
     (SELECT bl2.BANK_NAME, bl2.LOAN_NUMBER
      FROM BANK_LOANS
      WHERE bl2.MONTH_ID = 76  --max month id provided to query
     ) name
WHERE name.LOAN_NUMBER = bl.LOAN_NUMBER
ORDER BY name.BANK_NAME, bl.LOAN_NUMBER, bl.MONTH_ID DESC

Answer 1

with
     test_data ( month_id, loan_number, bank_name, amount ) as (
       select 76, '00-100', 'Bank One'    , 100.00 from dual union all
       select 75, '00-100', 'The Bank One', 150.00 from dual union all
       select 74, '00-100', 'Bank 1'      , 150.00 from dual union all
       select 76, '00-200', 'Another Bank', 300.00 from dual union all
       select 75, '00-200', 'Another Bank', 500.00 from dual
     )
-- end of test data (not part of the solution).
-- SQL query begins BELOW THIS LINE; use with your table.
select month_id, loan_number, 
       first_value(bank_name) 
              over (partition by loan_number order by month_id desc) as bank_name,
       amount
from   test_data
;

MONTH_ID LOAN_N BANK_NAME    AMOUNT
-------- ------ ------------ ------
      74 00-100 Bank One        150
      75 00-100 Bank One        150
      76 00-100 Bank One        100
      75 00-200 Another Bank    500
      76 00-200 Another Bank    300

5 rows selected.

Answer 2

Use analytic functions:

select bl.loannumber, bl.amount,
       max(bank_name) keep (dense_rank first order by month_id desc) over (partition by loannumber) as bank_name
from bank_loans bl;

Answer 3

SELECT month_id,
   loan_number,
   MIN(bank_name) over(PARTITION BY loan_number ORDER BY month_id DESC),
   amount
FROM bank_loans;