UNIQUE constraint failed: mytable.hostName

I have created my own table called mytable in sqlite and want to capture content of a list of my hosts and write them into table. I can get content of pages with python-requests but while reaching to a host the following error occurs:

UNIQUE constraint failed: mytable.hostName

Is this a problem with my table while creating it? I am creating the table like so:

> CREATE TABLE mytable (host CHAR(20) PRIMARY KEY, content TEXT);