SQL & PL/SQL

Hi,
Good day to everyone here. Im using Hands-on Oracle Database 10g for Linux, now in page 228. Im having a problem of loading a text file into the databases table. Here is my databases table.

SQL> DESC handsonxe06.databases;
Name Null? Type
----------------------------------------- -------- ----------------------------
DB_ID NOT NULL NUMBER(3)
DB_NAME NOT NULL VARCHAR2(100)
DB_VERSION VARCHAR2(25)
HOST_ID NOT NULL NUMBER(3)

Now I have a text file called DB1.csv and I want to load this records into my databases table. Here is my text file.

db_name db_version host_id
db1 10.2.0.1 1
db2 9.2.0.7 1
db3 10.2.0.1 1
db4 10.2.0.1 1
db5 9.2.0.7 1
db6 9.2.0.7 1
db7 9.2.0.7 1
db8 9.2.0.7 1
I did not include the DB_ID because the data load will rely on the newly created DATABASES_TPK trigger (db_id sequence) to automatically generate primary keys for each new record.

Now after I loaded this records into the databases table, error messages showed up like this:

This page displays information about text data file import. If any rows failed while importing, this page displays an error message.
Import Date 28-JAN-07
Imported By HANDSONXE06
Schema HANDSONXE06
Table DATABASES
Rows Imported 0
Rows Failed 8

Failed Rows
Error Data
ORA-01400: cannot insert NULL into ("HANDSONXE06"."DATABASES"."HOST_ID") Row 2: 'db1' '10.2.0.1' 1
ORA-01400: cannot insert NULL into ("HANDSONXE06"."DATABASES"."HOST_ID") Row 3: 'db2' '9.2.0.7' 1
ORA-01400: cannot insert NULL into ("HANDSONXE06"."DATABASES"."HOST_ID") Row 4: 'db3' '10.2.0.1' 1
ORA-01400: cannot insert NULL into ("HANDSONXE06"."DATABASES"."HOST_ID") Row 5: 'db4' '10.2.0.1' 1
ORA-01400: cannot insert NULL into ("HANDSONXE06"."DATABASES"."HOST_ID") Row 6: 'db5' '9.2.0.7' 1
ORA-01400: cannot insert NULL into ("HANDSONXE06"."DATABASES"."HOST_ID") Row 7: 'db6' '9.2.0.7' 1
ORA-01400: cannot insert NULL into ("HANDSONXE06"."DATABASES"."HOST_ID") Row 8: 'db7' '9.2.0.7' 1
ORA-01400: cannot insert NULL into ("HANDSONXE06"."DATABASES"."HOST_ID") Row 9: 'db8' '9.2.0.7' 1

I know I put data in the databases.host_id which is not null. Can anybody here explain to me what was really my big mistake in loading the records(DB1.csv) into the databases table. I would appreciate for some help please. Thank you very much.

regards,
jocelyn