WP custom admin columns

//DISPLAY CUSTOM POST COLUMNS
add_filter('manage_collections_posts_columns', 'manage_collections_columns');
add_action('manage_collections_posts_custom_column', 'print_collections_column', 10, 2);
 
function manage_collections_columns($existing_columns) {
  $existing_columns['_columnname'] = 'Column Name';
  return $existing_columns;
}
 
function print_collections_column($column_name, $post_id) {
  if( $column_name == '_columnname' ) {
    //do something
  }
}
 
 
//SORT BY CUSTOM POST COLUMNS
add_action( 'parse_request', 'mytest_parse_request' ); 
function mytest_parse_request( $wp ) { 
        global $wp_query; 
        $wp_query->is_main_loop = true; 
        return $wp; 
} 
 
if ( is_admin() ) add_filter('pre_get_posts', 'filter_by_issues');
function filter_by_issues($query) {
    global $wp_query;
    $posttype = $query->get('post_type');
    if($posttype == 'post' && isset($query->is_main_loop) && $query->is_main_loop) { 
        $value = $_GET['meta_value'];
    	$query->set('meta_key', 'meta_value' );
   		$query->set('meta_value', $value );
    }
 
    return $query;
}