C# MySql “Parameter '@??' must be defined”

C# 一段程序如下，执行出错，错误信息是

'@rowNum' must be defined”~~~

但是直接在 mySql workbatch 中运行是正确的！！ 原因何在？
搜索一下， 看到老外的网站说 连接串要加上 ： ~~~“Allow User Variables=True”,
再试验一次，发现可以了！！
string mySqlConnString = @"Database=testDB ; User Id = root; Password =password;Data source=10.10.10.107;";
MySql.Data.MySqlClient.MySqlConnection mySqlConn = new MySql.Data.MySqlClient.MySqlConnection();
mySqlConn.ConnectionString = mySqlConnString;
mySqlConn.Open();
MySql.Data.MySqlClient.MySqlCommand mySqlCmd = new MySql.Data.MySqlClient.MySqlCommand(); //declare @rowNumber as integer; mySqlCmd.Connection = mySqlConn;
mySqlCmd.CommandText = "set @rowNum:=0;
create temporary table T_729540255 as ( Select @rowNum:=ifnull(@rowNum,0)+1 as Temp_id, A.employee_id,A.employee_no From employee A)";
mySqlCmd.ExecuteNonQuery();