mysql replace into with SET-syntax overrides all fields - php

Question

I have the following query:
REPLACE INTO `oxarticles`
SET
OXID = '10-1010',
oxartnum = '10-1010',
oxtitle = 'Dummy',
oxprice = '10.000000',
oxstock = '100',
importstatus = 1"
This works so far as expected, but the fields I do not specifiy, are just overwritten with ' ' / empty string. From what I read, should this syntax work identically like the UPDATE-command.
Am I missing something? How can I prevent that fields are replaced with '' ?
Edit 1
Just to clarify, I can't just use UPDATE. I am setting a flag (importstatus) to 0 before every run and during the import to 1. After the import finishes, I delete all articles, which are still on status 0.
// Just for the compeletion, here is the PHP-snippet:
while (!feof($this->handle))
{
$row = fgetcsv($this->handle, 0, ";");
$sSql = "REPLACE INTO oxarticles SET "
. " OXID = '" . $row[0] . "', "
. " oxartnum = '" . $row[0] . "', "
. " oxtitle = '" . $row[1] . "', "
. " oxprice = '" . str_replace(",", ".", $row[4]) . "', "
. " oxstock = '" . str_replace(",", ".", $row[5]) . "', "
. " importstatus = 1";
// $sSql = "UPDATE oxarticles SET oxtitle ='" . $row[1] . "', oxprice='" . $row[4] . "', oxstock='" . $row[5] . "' WHERE oxartnum ='".$row[0]."'";
$this->db->execute($sSql);
}

Answer 1

From the mysql documentation:
REPLACE works exactly like INSERT, except that if an old row in the
table has the same value as a new row for a PRIMARY KEY or a UNIQUE
index, the old row is deleted before the new row is inserted. See
Section 13.2.5, “INSERT Syntax”.
In other words, the row is being deleted and then inserted, hence your old values aren't staying intact. Perhaps you could select the original row first, and feed those values back in where appropriate.

Answer 2

You query will replace old data into new data if you do not provide data for a field it will set to null . If you do not want to loose your data just want to update field use on duplicate key update.
If did't found any match it will insert new row
If found it will replace data if provide
INSERT INTO table (id,a,b,c,d,e,f,g) VALUES (1,2,3,4,5,6,7,8) ON
DUPLICATE KEY
UPDATE a=a, b=b, c=c, d=d, e=e, f=f, g=g;