WriteBack Report tries to UPDATE a new row

Question

I have created a new report that I have enabled WriteBack on. When updating existing items, all is OK. When I go to create a new item, it sometimes attempts to do an UPDATE rather than an INSERT ( which fails ). However, sometimes it works OK.
XML as follows:
<?xml version="1.0" encoding="utf-8" ?>
<WebMessageTables xmlns:sawm="com.siebel.analytics.web/message/v1">
<WebMessageTable lang="en-us" system="WriteBack" table="Messages">
<WebMessage name="WriteBack">
<XML>
<writeBack connectionPool="ConnectionPool">
<insert>INSERT INTO OBIEE_USERS (USERNAME, GROUPNAME, OFFICE_ID) VALUES ('@{c0}', '@{c1}', '@{c2}')</insert>
<update>UPDATE OBIEE_USERS SET GROUPNAME='@{c1}', OFFICE_ID='@{c2}' where USERNAME='@{c0}'</update>
</writeBack>
</XML>
</WebMessage>
</WebMessageTable>
</WebMessageTables>
The "ConnectionPool" is an Oracle XE connection and I have insert/update access to the file and I created an empty in the file with a USERNAME of "new" and nothing else so when I go to update it should see it as a new item (as the rest of the record is null ).
The log file for my session is definitely trying to UPDATE rather than INSERT:
-------------------- SQL Request:
EXECUTE PHYSICAL CONNECTION POOL ConnectionPool UPDATE OBIEE_USERS SET GROUPNAME='testgroup', OFFICE_ID='testoffice' where USERNAME='testuser'
+++Administrator:410000:410012:----01/03/2010 14:35:57
-------------------- Sending query to database named EPMUAT (id: ExecutePhysical Gateway):
UPDATE OBIEE_USERS SET GROUPNAME='testgroup', OFFICE_ID='testoffice' where USERNAME='testuser'
+++Administrator:410000:410012:----01/03/2010 14:35:57
-------------------- Query Status: Successful Completion
Can anyone point me to why this is happening or an alternative way to insert new items correctly.
Thanks

Answer 1

http://siebel.ittoolbox.com/groups/technical-functional/siebel-analytics-l/insert-and-update-for-the-writeback-1573962
you should have usename as null too instead of 'new'