必须定义Sql查询参数名称

您好我有这个SQL查询：

SQL = "SELECT SUM( " + "CASE WHEN rn =1" + "THEN v.FirstAmount" + "WHEN rn =2" + "THEN v.SecondAmount " + "ELSE v.ThirdAmount " + "END ) " + "FROM (" + "SELECT cv. * , @rn := IF( @vi = `Violation ID` , @rn +1, 1 ) AS rn, @vi := `Violation ID` " + "FROM class_violation cv" + "CROSS JOIN (" + "SELECT @rn :=0, @vi := ''" + ")CONST" + "ORDER BY `Violation ID`" + ")cv" + "JOIN violation v ON cv.`Violation ID` = v.`Violation ID` " + "JOIN class_record tr ON cv.`Class No.` = tr.`Class No.` " + "WHERE tr.`Class ID` = '" + where + "'"; 

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我收到这个错误：

 MySql.Data.MySqlClient.MySqlException: Fatal Error encountered during command execution ---> MySql.Data.MySqlClient.MySqlException: Parameter '@rn' must be defined at MySql.Data.MySqlClient.Statement.SerializeParameter(MySqlParameterCollection parameters, MySqlPacket packet, String parmName, Int32 parameterIndex) at MySql.Data.MySqlClient.Statement.InternalBindParameters(String sql, MySqlParameterCollection parameters,MySqlPacket packet) 

我如何更正我的SQL查询并定义参数？

Answer 1

我想我知道如何回答我的问题。 在我的连接字符串中，我刚刚添加了Allow User Variables = True，它现在可以正常工作了！