MySQL error(2014) Commands out of sync; you can't run this command now(情形1)

错误出现在调用了存储过程之后继续调用了返回结果集的命令。

这个错误的官方解释为：

If you get Commands out of sync; you can’t run this command now in your client code, you are calling client functions in the wrong order.

This can happen, for example, if you are using mysql_use_result() and try to execute a new query before you have called mysql_free_result().

It can also happen if you try to execute two queries that return data without calling mysql_use_result() or mysql_store_result() in between.

地址为：Commands out of sync

执行了一个存储过程，需要将结果集取完，然后才能调用下一个返回结果集的命令。

示例如下(Connector/C++中的处理办法)：

存储过程：

BEGINselect * from gamebase where Accountid = AccID;
END

代码片段1：

newConnection.SetStatement("CALL LoadGameBase(1)");
newConnection.Execute();auto resultSet = newConnection.GetResultSet();
while (resultSet.Next())
{int accountID = resultSet.GetInt(1);std::string accountName = resultSet.GetString(2);double curGold = resultSet.GetDouble(3);std::cout << accountID << " " << accountName << " " << curGold << std::endl;
}

上面这种执行方式就会报错为"Commands out of sync…"

正确的方式为：
代码片段2：

newConnection.SetStatement("CALL LoadGameBase(1)");
newConnection.Execute();do
{auto resultSet = newConnection.GetResultSet();while (resultSet.Next()){int accountID = resultSet.GetInt(1);std::string accountName = resultSet.GetString(2);double curGold = resultSet.GetDouble(3);std::cout << accountID << " " << accountName << " " << curGold << std::endl;}
}
while (newConnection.GetMoreResults());

使用成员函数GetMoreResults遍历结果集。
注意上面GetMoreResults的调用方式，
只能使用do、while，这是因为调用GetMoreResults之前，"结果集指针"就已经指向了第一个结果集，
调用之后，将会指向下一个。

下面是错误示例：
代码片段3：

newConnection.SetStatement("CALL LoadGameBase(1)");
newConnection.Execute();while (newConnection.GetMoreResults())
{auto resultSet = newConnection.GetResultSet();while (resultSet.Next()){int accountID = resultSet.GetInt(1);std::string accountName = resultSet.GetString(2);double curGold = resultSet.GetDouble(3);std::cout << accountID << " " << accountName << " " << curGold << std::endl;}
}

执行后不会报错，但也不会得到任何数据。

还有一点需要注意：
如果执行完存储过程后，完全不取结果集，是可以直接执行下一个返回结果集的语句。
可以理解为：存储过程返回的结果集，要么不取，要么取完。

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