How to get all the related ids without array?

Question

I want to get all the post ids when the post meta includes a key of "project_id". This function get the job down, but need refine:

function get_all_ids(){
global $wpdb, $post;
$meta_key1 = 'project_id';
$postids = $wpdb->get_col( $wpdb->prepare( "
    SELECT key1.post_id
    FROM $wpdb->postmeta key1
    WHERE key1.meta_key = %s",$meta_key1 ) );
return $postids;
}

This returns arrays of (0 =>1), ( 1 =>3 ), (2 =>5) In the later step, I will need to get the ids like this:

$this->results = $projects->get_all_ids();

This requires the ids are not arrays. How can I get all the ids without array?

Answer 1

If you need the ids separated by coma you can get them from the array you have:

$listids = implode ( "," , $postids );

In any case, please provide more info or code about what you need