It seems netezza cross-database access is readonly: it won't work in insert, update, or delete statements.

At least that is what I conclude from this IBM doc page which says:

"You cannot use a cross-database INSERT, UPDATE, or DELETE statements to change a table in a different, remote, database. If you attempt a cross-database write operation, the system displays an error message.

For example:

DEV.DBUSER(DBUSER)=>INSERT INTO prod..emp SELECT * FROM newusers;
Cross Database Access not supported for this type of command."
[download]

So I think you just have to remove the 'dbname.' part from the statement so that netezza won't think it is asked to do (illegal) cross database access.

update: (Having no Netezza here, I tried to recreate the error on Postgres (on which Netezza was based albeit a long time ago [1]). Postgres doesn't have cross-database access at all, not even readonly. Postgres still shows a similar error message when asked to access another database:

(Pg 9.5devel, HEAD dcbf5948e12a)

$ psql -d testdb
psql (9.5devel)
Type "help" for help.

testdb=# create table t(c text);
CREATE TABLE

testdb=# insert into t values ('value 1');
INSERT 0 1

testdb=# insert into test.public.t values ('value 3');
ERROR:  cross-database references are not implemented: "test.public.t"
LINE 1: insert into test.public.t values ('value 2');
[download]

)