sql - 仅在 SQL 中根据条件删除表中的重复项

Question

假设我有一个包含列的表：

CustomerNumber
Lastname
Firstname
PurchaseDate

...以及其他列如果未在此处显示，则不会更改问题中的任何内容。

在此表中，我可以为具有不同购买日期的同一客户提供许多行（我知道，设计不佳......我只是试图解决报告问题，而不是真正试图解决问题的根源）。

如何在 SQL 中为每个客户保留一条记录的最新日期，然后删除其余记录？Agroup by似乎不适用于我的情况

Answer 1

;with a as
(
select row_number() over (partition by CustomerNumber, Lastname, Firstname order by PurchaseDate desc) rn
from <table>
)
delete from a where rn > 1

Answer 2

这对我有用（在 DB2 上）：

 DELETE FROM my_table 
 WHERE (CustomerNumber, Lastname, Firstname, PurchaseDate) 
 NOT IN ( 
       SELECT CustomerNumber, Lastname, Firstname, MAX(PurchaseDate) 
       FROM my_table 
       GROUP BY CustomerNumber, Lastname, FirstName 
 )

Answer 3

SELECT CustomerNumber, Lastname, Firstname, MAX(PurchaseDate) LatestPurchaseDate
FROM Table
GROUP BY CustomerNumber, Lastname, Firstname

MAX 将选择最高（最新）日期，并为 GROUP BY 列的每个唯一组合显示该日期。

编辑：我误解了您想删除除最新购买日期之外的所有记录。

WITH Keep AS
(
    SELECT CustomerNumber, Lastname, Firstname, MAX(PurchaseDate) LatestPurchaseDate
    FROM Table
    GROUP BY CustomerNumber, Lastname, Firstname
)
DELETE FROM Table
WHERE NOT EXISTS
(
    SELECT *
    FROM Keep
    WHERE Table.CustomerNumber = Keep.CustomerNumber
    AND Table.Lastname = Keep.Lastname
    AND Table.Firstname = Keep.Firstname
    AND Table.PurchaseDate = Keep.LastPurchaseDate
)