Question

Let’s say I have a table with columns:

CustomerNumber
Lastname
Firstname
PurchaseDate

…and other columns that do not change anything in the question if they’re not shown here.

In this table I could have many rows for the same customer with different purchase dates (I know, poorly designed… I’m only trying to fix an issue for reporting, not really trying to fix the root of the problem).

How, in SQL, can I keep one record per customer with the latest date, and delete the rest? A group by doesn’t seem to be working for my case

Answer 1

This worked for me (on DB2):

 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 
 )