MYSQL - empty string == 0 problem (updates row with primary key 0 instead of insert)

Question

actually this already worked and i have no idea what i've changed so that i run into this problem now. Tried nearly everything.

The case:
I have the following query. The variable $DB-id is an empty string if the content i want to save is new. The field module_id is my primary key. What happens is that this query always updates the row with the module_id => 0.

The problem
Passing an empty variable as the primary key always updates row 0 instead of inserting a new one.

$this->db->query("INSERT INTO   modules_text 
                                (   
                                module_id,
                                module_content,
                                module_page_idx, 
                                module_post_id
                                )
                  VALUES        (
                                '{$DB_id}',
                                '{$content['text']}',
                                '{$content['idx']}',
                                '{$post_id}'
                                )
                  ON DUPLICATE KEY
                  UPDATE        module_content  = '{$content['text']}',
                                module_page_idx = '{$content['idx']}'
                ");

Does anybody have an idea how i can tell MYSQL to create a new row??? Any help is very appreciated!!!! Thank you very much!!!

Saludos Sacha!

Answer 1

You may need to set your primary key field to auto increment. An example is below.

CREATE TABLE tablename (
 id MEDIUMINT NOT NULL AUTO_INCREMENT,
 name CHAR(30) NOT NULL,
 PRIMARY KEY (id)) 

Answer 2

I would assume you need to give the UPDATE a WHERE?
eg:

$this->db->query("INSERT INTO   modules_text 
                                (   
                                module_id,
                                module_content,
                                module_page_idx, 
                                module_post_id
                                )
                  VALUES        (
                                '{$DB_id}',
                                '{$content['text']}',
                                '{$content['idx']}',
                                '{$post_id}'
                                )
                  ON DUPLICATE KEY
                  UPDATE        `module_content`  = '{$content['text']}',
                                `module_page_idx` = '{$content['idx']}'
                  WHERE
                                `module_id` = '{$content['id']}'
                ");

Don't hold me to it xD, just a guess at first glance.