src/db/BuildSql.php
public static function getInstance($dbConfig = '')
    {
        if (is_null(self::$instance)) {
            self::$instance = new BuildSql($dbConfig);
        }

        return self::$instance;

    }
public static function getInstance($dbConfig = '')
    {
        if (is_null(self::$instance)) {
            self::$instance = new BuildSql($dbConfig);
        }

        return self::$instance;

    }
单例实例化 避免重复New暂用资源