Mysql insert into identical table

[Anon]

                       The original select: 
                       select username,uid from db1.user LEFT JOIN db2.user on
                       db1.user.userid=db2.user.userid where db1.user.username is NULL; 

                       This gives me the 65 missing usernames from db1.user that need to be inserted into
                       db2.user. 

                       I use this insert statement: 

                       Insert into db2.user select * from db1.user LEFT JOIN db2.user on
                       db1.user.userid=db2.user.userid where db1.user.username is NULL; 

                       because db1.user and db2.user are identical in structure, this should work but the
                       error I get is 
                       ERROR 1066: Not unique table/alias: 'user' 

                       There are 35 columns in these tables and I've tried listing the columns in the
                       insert and select statement but I get the same error. Any clue? 

                       Thanks