当GROUP_CONCAT返回BLOB时，Convert.ToString返回`System.Byte []`而不返回实际数据

Question

我有一种方法是调用 MySQL 程序。以下是程序的一部分：

SELECT AR.alert_id AS AlertId,
        AR.rule_id AS RuleId,
        AR.name AS RuleName,
        AR.rule_type AS RuleType, 
        AR.description AS Description, 
        (SELECT group_concat(occured_event_id separator ', ') 
            FROM alert_rule_event
            WHERE alert_rule_id = AR.id) AS OccuredEventIds,
FROM alert_rule AR

C＃代码：

alertRuleEntity.AlertId = Convert.ToInt32(dtAlertRuleEntityList.Rows[index]["AlertId"]);
alertRuleEntity.RuleId = Convert.ToInt32(dtAlertRuleEntityList.Rows[index]["RuleId"]);
alertRuleEntity.RuleName = Convert.ToString(dtAlertRuleEntityList.Rows[index]["RuleName"]);
alertRuleEntity.RuleType = Convert.ToString(dtAlertRuleEntityList.Rows[index]["RuleType"]);
alertRuleEntity.Description = Convert.ToString(dtAlertRuleEntityList.Rows[index]["Description"]);
alertRuleEntity.OccuredEventIds = Convert.ToString(dtAlertRuleEntityList.Rows[index]["OccuredEventIds"]);

返回值如下：

能够正确读取所有列值。但是对于列OccuredEventIds，它的值为System.Byte[]而不是实际值。可能是什么问题？

Answer 1

在对我的程序进行以下更改后，它起作用了：

(SELECT group_concat(CONVERT(occured_event_id, CHAR(8)) separator ', ') 
FROM alert_rule_event
WHERE alert_rule_id = AR.id) AS OccuredEventIds

Answer 2

我会先尝试将参数转换为group_concat至varchar作为documentation says that it converts binary parameters至BLOB。

SELECT AR.alert_id AS AlertId,
        AR.rule_id AS RuleId,
        AR.name AS RuleName,
        AR.rule_type AS RuleType, 
        AR.description AS Description, 
        (SELECT group_concat(cast(occured_event_id as char(20)) separator ', ') 
            FROM alert_rule_event
            WHERE alert_rule_id = AR.id) AS OccuredEventIds,
FROM alert_rule AR

Answer 3

Group_Concat返回BLOB类型，只有你得到Bytes作为输出，

Sol-1：

将group_concat_max_len系统变量的值更改为512 并重新启动MySql服务

请参阅此处： Why GROUP_CONCAT returns BLOB?

OR

Sol-2：

在您的连接字符串中设置"respect binary flags=false;"

希望这可以帮助你......