从查询中检索单个值

Question

我正在尝试根据字符串字段用户名从单个表中检索整数值.我已经尝试使用存储过程和直接文本.当我执行存储过程时,我得到正确的返回值; 然而,正确的结果并没有通过.

以下是两组代码 - 直接文本 -

public int GetUserRole(string CUSER)
{
    try
    {
        SQLCON = new SqlConnection(connectionString);
        SQLCON.Open();
        SQLCommand = new SqlCommand();
        SQLCommand.CommandType = CommandType.Text;
        SQLCommand.Parameters.Add("USUsername", SqlDbType.VarChar).Value = CUSER;
        SQLCommand.CommandText = "SELECT USRole FROM tblUser WHERE USUsername = CUSER";
        Int32 USRole = (Int32) SQLCommand.ExecuteScalar();

        return USRole;

    }
    catch
    {
        HttpContext.Current.Response.Redirect("~/ErrorRedirect.aspx", false);
        return 0;
    }
}

SQL查询:

ALTER PROCEDURE [dbo].[spGetUserRole]
-- Add the parameters for the stored procedure here
    @username VARCHAR(50)
AS
BEGIN
-- Declare the return variable here
DECLARE @USRole as int

-- Add the T-SQL statements to compute the return value here
SELECT @USRole = tblUser.USRole FROM tblUser WHERE USUsername = @username

-- Return the result of the function
RETURN @USRole  
END

Answer 1

您没有正确引用参数.如果要添加名为USUsername的参数,则在命令文本中应使用@USUsername:

public int GetUserRole(string CUSER)
{
    try
    {
        SQLCON = new SqlConnection(connectionString);
        SQLCON.Open();
        SQLCommand = new SqlCommand();
        SQLCommand.CommandType = CommandType.Text;
        SQLCommand.Parameters.Add("USUsername", SqlDbType.VarChar).Value = CUSER;
        SQLCommand.CommandText = "SELECT USRole FROM tblUser WHERE USUsername = @USUsername";
        Int32 USRole = (Int32) SQLCommand.ExecuteScalar();

        return USRole;

    }
    catch (Exception)
    {
        HttpContext.Current.Response.Redirect("~/ErrorRedirect.aspx", false);
        return 0;
    }
}

您的存储过程也需要更新,因为此处的参数名称也应该匹配,并且您不需要返回变量.

ALTER PROCEDURE [dbo].[spGetUserRole]
-- Add the parameters for the stored procedure here
@USUsername VARCHAR(50)

AS
BEGIN

-- Add the T-SQL statements to compute the return value here
SELECT tblUser.USRole FROM tblUser WHERE USUsername = @USUsername

END

您还应该使用"using"语法来自动关闭数据库连接.请参阅Scott Hanselman的示例 - http://www.hanselman.com/blog/WhyTheUsingStatementIsBetterThanASharpStickInTheEyeAndASqlConnectionRefactoringExample.aspx