nodejs读取数据库的一种写法

MySQLStore.prototype.createDatabaseTable = function(cb) {

    debug_log('Creating sessions database table');

    var fs = require('fs');
    /**读取当前目录下上级目录中的schema.sql中sql语句*/
    /**

        CREATE TABLE IF NOT EXISTS `sessions` (
      `session_id` varchar(255) COLLATE utf8_bin NOT NULL,
      `expires` int(11) unsigned NOT NULL,
      `data` text,
      PRIMARY KEY (`session_id`)
    ) ENGINE=InnoDB  DEFAULT CHARSET=utf8 COLLATE=utf8_bin

    */
    fs.readFile(__dirname + '/../schema.sql', 'utf-8', function(error, sql) {

        if (error) {
            return cb(error);
        }
          // '??' 变成 ??
        sql = sql.replace(/`[^`]+`/g, '??');

        var params = [
            this.options.schema.tableName,
            this.options.schema.columnNames.session_id,
            this.options.schema.columnNames.expires,
            this.options.schema.columnNames.data,
            this.options.schema.columnNames.session_id
        ];
        //创建sessions表，有列session_id，expires，data
        this.connection.query(sql, params, function(error) {

            if (error) {
                debug_error('Failed to create sessions database table.');
                debug_error(error);
                return cb && cb(error);
            }

            cb && cb();
        });

    }.bind(this));
};