WP Custom Sortable Columns

add-sortable-column.php

<?php

//-----Add sortable columns
function sortable_column_func(){
	return array(
	'my_sortable_variable' => 'my_sortable_variable',
	);
}
add_filter("manage_edit-POST_TYPE_NAME_sortable_columns", "sortable_column_func");

function sorting_column_orderby( $vars ) {	
	if ( (!isset($vars['orderby']) && 'POST_TYPE_NAME' == $vars['post_type']) || (isset( $vars['orderby'] ) && 'my_sortable_variable' == $vars['orderby']) ) {
		$vars = array_merge( $vars, array(
			'meta_key' => 'my_sortable_variable',
			'orderby' => 'meta_value'
		) );
	} 
	 
	return $vars;
}
add_filter( 'request', 'sorting_column_orderby' );

?>