Confusion over relationship of wp_post and wp_postmeta tables

Hello all,

I am confused over the relationship of the wp_posts and wp_postmeta tables.

I would like to select all the posts from wp_posts, which do not have a custom field ( which I have created ) in the wp_postmeta table. I had been assuming that ‘ID’ in wp_posts is the primary key and that ‘post_id’ in wp_postmeta corresponds to it, but I’m no longer sure that this is the case.

If this is not the case , then how does one link the 2 tables?

I have been experimenting with the following query:

$postIDs =  $wpdb->get_col("SELECT ID FROM $wpdb->posts INNER JOIN $wpdb->postmeta ON  ID=post_id WHERE meta_key<>'keyword'");

this returns the correct post_ids from the wp_postmeta table.

However I am looking for The IDs from the wp_posts table.

Any ideas on how to write a query to get the latter?

Thanks in advance,

KC