Source

File: wp-includes/class-wp-comment-query.php

protected function get_search_sql( $string, $cols ) {
		global $wpdb;

		$like = '%' . $wpdb->esc_like( $string ) . '%';

		$searches = array();
		foreach ( $cols as $col ) {
			$searches[] = $wpdb->prepare( "$col LIKE %s", $like );
		}

		return ' AND (' . implode( ' OR ', $searches ) . ')';
	}