MySql output c#中的参数

Question

I'm running the following code, that is meant to execute SET @Param = 3; line in MySql, and get Param value 3.

MySqlCommand setCommand = new MySqlCommand("SET @Param = 3;", connection);

MySqlParameter parameter = new MySqlParameter("Param", MySqlDbType.Int32);
parameter.Direction = System.Data.ParameterDirection.Output;
setCommand.Parameters.Add(parameter);

setCommand.ExecuteNonQuery();

Console.WriteLine("Parameter value: "+parameter.Value);

I'm quite new to MySql, but as far as I understood, the query SET @Param = 3; sets the @Param variable value to 3, and apart from my c# code it looks like it's working (in separate workbench). But when running my code it throws the following error:

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'NULL = 3' at line 1

I believe that when trying to run this query SET @Param = 3; it tries to fill @Param parameter that is null, instead of getting it's value. I've declared parameters Direction as Output and added it to the setCommand command Parameters, but it seems like I'm doing something wrong. I don't know where am I wrong, is it Direction issue, the @/?/none parameter declaration issue, or maybe it is MySqlDbType issue (as I'm not sure that MySqlDbType.Int32 corresponds to Int32 in C#)? Please advise.

Answer 1

It should be working in MS SQL, I've used it's tutorial and adapted it for MySql. After some research I've found a similar reported issue. In MySql, it seems that Direction property of Parameter can't be Output if CommandType is Text - @parameter s wouldn't be output as intended. You can set this property though, it just wouldn't work. The resolution might be executing SELECT @parameter; after executing the main SET/UPDATE/etc. parametrized queries to get values, or creating Stored Procedures.

Reference: https://github.com/mysql.net/MySqlConnector/issues/231