Source

File: wp-includes/post.php

function _filter_query_attachment_filenames( $clauses ) {
	global $wpdb;
	remove_filter( 'posts_clauses', __FUNCTION__ );

	// Add a LEFT JOIN of the postmeta table so we don't trample existing JOINs.
	$clauses['join'] .= " LEFT JOIN {$wpdb->postmeta} AS sq1 ON ( {$wpdb->posts}.ID = sq1.post_id AND sq1.meta_key = '_wp_attached_file' )";

	$clauses['groupby'] = "{$wpdb->posts}.ID";

	$clauses['where'] = preg_replace(
		"/\({$wpdb->posts}.post_content (NOT LIKE|LIKE) (\'[^']+\')\)/",
		'$0 OR ( sq1.meta_value $1 $2 )',
		$clauses['where']
	);

	return $clauses;
}