如何通过c#修复SQL查询中的错误“必须声明标量变量”？

Question

我不断收到这个烦人的错误。我对 SQL 真的很陌生，这实际上是我的第一个查询，但我无法让它工作。我已经尝试了几个小时。请帮忙！

我得到错误：

System.Data.SqlClient.SqlException: '必须声明标量变量“@FirstNamez”。

代码：

public static void CreateNewEmployee(string FirstNamez, string LastNamez, int Pinz, string Departmentz)
{
    SqlConnection connection = new SqlConnection();
    connection.ConnectionString = @"Server = localhost\SQLEXPRESS; Database = Employee; Trusted_Connection = True;";

    SqlCommand command = new SqlCommand();

    using (connection)
    {
        connection.Open();
        string commandtext = "INSERT INTO dbo.EmployeeDatabase (FirstName, LastName, PIN, Department) VALUES (@FirstNamez, @Lastnamez, @Pinz, @Departmentz);";

        command.CommandText = commandtext;
        command.Connection = connection;

        command.ExecuteNonQuery();
    }
}

Answer 1

您在查询文本中定义所有参数 - 但您永远不会设置它们的值！

试试这个：

public static void CreateNewEmployee(string FirstNamez, string LastNamez, int Pinz, string Departmentz)
{
    SqlConnection connection = new SqlConnection();
    connection.ConnectionString = @"Server = localhost\SQLEXPRESS; Database = Employee; Trusted_Connection = True;";

    SqlCommand command = new SqlCommand();

    using (connection)
    {
        connection.Open();
        string commandtext = "INSERT INTO dbo.EmployeeDatabase (FirstName, LastName, PIN, Department) VALUES (@FirstNamez, @Lastnamez, @Pinz, @Departmentz);";

        command.CommandText = commandtext;
        command.Connection = connection;

        // define the parameters and set their values!
        command.Parameters.Add("@FirstNamez", SqlDbType.VarChar, 100).Value = FirstNamez;
        command.Parameters.Add("@LastNamez", SqlDbType.VarChar, 100).Value = LastNamez;
        command.Parameters.Add("@Pinz", SqlDbType.Int).Value = Pinz;
        command.Parameters.Add("@Departmentz", SqlDbType.VarChar, 100).Value = Departmentz;

        command.ExecuteNonQuery();
    }
}

Answer 2

您没有指定参数的值。查看这篇文章，了解如何将参数值添加到命令中： https://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlcommand.parameters(v=vs.110).aspx

Answer 3

使用以下代码：

在您的数据库中创建存储过程，而不是像这样的 AdHoc 查询：

CREATE PROC spAddNewEmployee
@FirstNamez nvarchar(100),
@Lastnamez nvarchar(100),
@Pinz nvarchar(100),
@Departmentz nvarchar(100)

AS

BEGIN
    INSERT INTO dbo.EmployeeDatabase (FirstName, LastName, PIN, Department) 
    VALUES (@FirstNamez, @Lastnamez, @Pinz, @Departmentz)
END

添加您的 C# 代码：

public static void CreateNewEmployee(string FirstNamez, string LastNamez, int Pinz, string Departmentz)
     {
        SqlConnection connection = new SqlConnection();
        connection.ConnectionString = @"Server = localhost\SQLEXPRESS; Database = Employee; Trusted_Connection = True;";

        SqlCommand cmd = new SqlCommand("spAddNewEmployee", connection);
        cmd.CommandType = CommandType.StoredProcedure;
        cmd.Parameters.AddWithValue("@FirstNamez", FirstNamez);
        cmd.Parameters.AddWithValue("@Lastnamez ", Lastnamez );
        cmd.Parameters.AddWithValue("@Pinz ", Pinz );
        cmd.Parameters.AddWithValue("@Departmentz ", Departmentz );

        connection.Open();
        cmd.ExecuteReader();
        connection.Close();

    }