INNER JOIN可以用同一個表中的另一個值替換列的值 - 對於所有行

Question

我需要編寫一個查詢來將列中的一個值替換為同一個表中另一行的值。 我試圖使用一個簡單的內連接，但我沒有看到我需要的結果。

這是BANK_LOANS表的一個例子：

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

數據是從外部來源加載的，不會驗證銀行名稱，因此給定貸款號碼的銀行名稱的拼寫可能會有所不同。 客戶希望BANK_NAME在數據庫中的任何內容，最大MONTH_ID用於該LOAN_NUMBER的所有結果，並且他們希望結果按BANK_NAME排序。 因此，例如，貸款00-100需要所有行的BANK_NAME為“Bank One”。

我嘗試使用內部聯接來執行此操作，但未獲得正確的結果

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

我想我有一個子查詢，但它有點難看。 我想知道是否有更好的方法（最佳實踐）通過連接或其他oracle函數來實現這一點。

這似乎有效，但它只是錯了：

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

使用分析函數：

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;