Remove duplicate rows, except one, ** where rows contain NULL values **

Question

This question is similar to but different from other SO questions involving removal of duplicate rows in MySQL.

Chosen solutions in the referenced questions(below) fail where one or more of the columns contain NULL values. I'm including schema as well as two chosen answers in a sqlfiddle below, to illustrate where the previous solutions are not working.

Source schema:

CREATE TABLE IF NOT EXISTS `deldup` (
  `or_id` int(11) NOT NULL AUTO_INCREMENT,
  `order_id` varchar(5) NOT NULL,
  `txt_value` varchar(20) NOT NULL,
  `date_of_revision` date NOT NULL,
  `status` int(3) DEFAULT NULL,
  PRIMARY KEY (`or_id`)
) ENGINE=MyISAM  DEFAULT CHARSET=latin1 AUTO_INCREMENT=16 ;

INSERT INTO `deldup` (`or_id`, `order_id`, `txt_value`, `date_of_revision`, `status`) VALUES
(1, '10001', 'ABC', '2003-03-06', NULL),
(2, '10001', 'RFE', '2003-03-11', NULL),
(3, '10002', 'ASE', '2009-08-05', NULL),
(4, '10003', 'PEF', '2001-11-03', NULL),
(5, '10004', 'OIU', '1999-10-29', NULL),
(6, '10005', 'FOO', '2002-03-01', NULL),
(7, '10006', 'RTY', '2005-08-19', NULL),
(8, '10001', 'NND', '2003-03-20', NULL),
(9, '10005', 'VBN', '2002-02-19', NULL),
(10, '10002', 'AAQ', '2009-08-13', NULL),
(11, '10002', 'EEW', '2009-08-07', NULL),
(12, '10001', 'ABC', '2003-03-06', 3),
(13, '10001', 'ABC', '2003-03-06', 3),
(14, '10001', 'ABC', '2003-03-06', NULL),
(15, '10001', 'ABC', '2003-03-06', NULL);

Solution Example 1:

http://sqlfiddle.com/#!2/983f3/1

create temporary table tmpTable (or_id int);

insert  tmpTable
        (or_id)
select  or_id
from    deldup yt
where   exists
        (
        select  *
        from    deldup yt2
        where   yt2.txt_value = yt.txt_value

                and yt2.order_id = yt.order_id
                and yt2.date_of_revision = yt.date_of_revision
                and yt2.status = yt.status
                and yt2.or_id > yt.or_id
        );

delete  
from    deldup
where   or_id in (select or_id from tmpTable);

Note that the rows containing non-null row values are successfully deleted, however rows containing null values are not removed (See row 14 and 15 in the resulting SELECT query).

---

Solution Example 2:

http://sqlfiddle.com/#!2/8a4f8/1

DELETE 
    n1 
FROM 
    deldup n1, 
    deldup n2 
WHERE 
    n1.or_id                < n2.or_id AND 
    n1.order_id             = n2.order_id AND 
    n1.txt_value            = n2.txt_value AND 
    n1.date_of_revision     = n2.date_of_revision AND
    n1.status               = n2.status 

This solution involves less code and works just the same as Example 1, including the exclusion of rows containing null values.

---

How can I remove the duplicate rows where one of the column values contains NULL values?

---

References:

Delete all Duplicate Rows except for One in MySQL?

Remove duplicate rows in MySQL

How to remove duplicate entries from a mysql db?

Answer 1

How about simply adjusting the second solution with something like this:

WHERE
  ...
  (n1.status IS NULL AND n2.status IS NULL 
   OR n1.status = n2.status)

I assume you consider the record a duplicate only if all values are repeated.