Select row based on max date across several columns

Question

For a mysql database

I have a table which includes duplicate rows because of date values in several columns. I am looking to select a single row for each unique customer id based on a max date value evaluated across several date columns

[customer id, startDate, StopDate, modifyDate, buyDate]

For each customer id, i'd like to return the row that has the maximum date either in the startDate, StopDate, modifyDate or buyDate columns ( there are some nulls in the date columns.

editing to include example - but to sure how to create a table here:

*** Edit

Been trying for quite awhile now to create a table here with an example. can't figure out. So posting an image? the desired rows to the returned indicated in red.

Answer 1

Assuming that the values are never NULL, you can use greatest():

select t.*
from table t
where greatest(t.startDate, stopDate, buyDate) =
          (select max(greatest(t.startDate, stopDate, buyDate))
           from t t2
           where t2.customerid = t.customerid
          );

Note: this will return multiple rows for a customer if more than one row contains the maximum date.