没有计数数据表对象

Question

I want to check if there exist any record in the query.

So what I tried is

 DataTable dtmkeylength = new DataTable("select count(lease_no) from XXACL_PROSPECTIVE_DATA_SAVE where mkey = " + Request.QueryString["userid"].ToString() + "");

        if (dtmkeylength.Rows.Count > 0)
        {
            HidMode.Value = "M";
            HidMKey.Value = dtmkeylength.Rows[0]["Mkey"].ToString();
        }

The below datatable object has count of 2 records into the database, but still it is not going inside IF condition.

WHY ?

Answer 1

in your query add the "as NNN" thing:

...select count(lease_no) as result...

so you can reference it by name.

Then, when you query, you can type:

dtmkeylength.Rows[0]["result"]

I hope that fixes it for you :)

EDIT

var userId = Request.QueryString["UserId"];

if(string.IsNullOrEmpty(userId)){
  throw new Exception("No UserID = no fun!");
}

DataTable dtmkeylength = new DataTable("select count(lease_no) from XXACL_PROSPECTIVE_DATA_SAVE where mkey =" + Request.QueryString["userid"].ToString() + "");

        if (dtmkeylength.Rows.Count > 0)
        {
            HidMode.Value = "M";
            HidMKey.Value = dtmkeylength.Rows[0][0].ToString();
        }

Answer 2

I think a better approach is to use ExecuteScalar , since you are using only the count.

using (SqlConnection conn = new SqlConnection(connString))
{
    String sql = "select count(lease_no) from XXACL_PROSPECTIVE_DATA_SAVE where mkey = @mkey";
    SqlCommand cmd = new SqlCommand(sql, conn);
    cmd.Parameters.Add("@mkey", (int) Request.QueryString["userid"]);

    try
    {
        conn.Open();
        int rowCount = (int) cmd.ExecuteScalar();

        if (rowCount  > 0)
        {
            HidMode.Value = "M";
            HidMKey.Value = dtmkeylength.Rows[0]["Mkey"].ToString();
        }
    }
    catch (Exception ex)
    {
        Console.WriteLine(ex.Message);
    }
}

Also note the parameterized query - @mkey is provided as a parameter and string concatenation is not used (this may lead to Sql Injection)

Answer 3

Try this:

static void Main(string[] args)
        {
            string param = "VINET";//your param here
            string conStr = ConfigurationManager.ConnectionStrings["conStr"].ConnectionString;
            using(SqlConnection  conn = new SqlConnection(conStr))
            {
                conn.Open();
                //modify your command on below line
                SqlCommand cmd = new SqlCommand("select count(OrderId) from Orders where CustomerID='" + param + "'");
                cmd.Connection = conn;
                SqlDataAdapter da = new SqlDataAdapter(cmd);
                DataSet ds = new DataSet();
                da.Fill(ds);
                conn.Close();
                if(ds.Tables[0].Rows.Count > 0)
                {
                    //do other staff
                }
            }
        }   

*Please follow commented lines

Edit
Below is a debug screen shot of your way of populating data table. As you can see, dt is detecting the command as table name and NOT as command.

Answer 4

It WILL always return rows even if the row count is zero.

try

int number = dtmkeylength.Rows[0].Field<int>(0);

if (number > 0)
{
...
}

Answer 5

There is no constructor for DataTable that takes a select statement, thats why it is empty, nothing selected yet!

The available constructor overloads available are the below three:

System.Data.DataTable dtmkeylength = new System.Data.DataTable();

Or

System.Data.DataTable dtmkeylength = new System.Data.DataTable("TableName);

Or

System.Data.DataTable dtmkeylength = new System.Data.DataTable("TableName", "tableNameSpace");

Check this and this example of how to use a DataTable