Handling ExecuteScalar() when no results are returned

Question

I am using the following SQL query and the ExecuteScalar() method to fetch data from an Oracle database:

sql = \"select username from usermst wh         


        

Answer 1

this could help .. example::

using System;
using System.Data;
using System.Data.SqlClient;

class ExecuteScalar
{
  public static void Main()
  {
    SqlConnection mySqlConnection =new SqlConnection("server=(local)\\SQLEXPRESS;database=MyDatabase;Integrated Security=SSPI;");
    SqlCommand mySqlCommand = mySqlConnection.CreateCommand();
    mySqlCommand.CommandText ="SELECT COUNT(*) FROM Employee";
    mySqlConnection.Open();

    int returnValue = (int) mySqlCommand.ExecuteScalar();
    Console.WriteLine("mySqlCommand.ExecuteScalar() = " + returnValue);

    mySqlConnection.Close();
  }
}

from this here

Answer 2

private static string GetUserNameById(string sId, string connStr)
    {
        System.Data.SqlClient.SqlConnection conn = new System.Data.SqlClient.SqlConnection(connStr);
        System.Data.SqlClient.SqlCommand command;

        try
        {
            // To be Assigned with Return value from DB
            object getusername;

            command = new System.Data.SqlClient.SqlCommand();

            command.CommandText = "Select userName from [User] where userid = @userid";

            command.Parameters.AddWithValue("@userid", sId);

            command.CommandType = CommandType.Text;

            conn.Open();

            command.Connection = conn;

            //Execute
            getusername = command.ExecuteScalar();

            //check for null due to non existent value in db and return default empty string
            string UserName = getusername == null ? string.Empty : getusername.ToString();

            return UserName;


        }
        catch (Exception ex)
        {

            throw new Exception("Could not get username", ex);
        }
        finally
        {
            conn.Close();
        }

    }

Answer 3

Try this

sql = "select username from usermst where userid=2"

string getusername = Convert.ToString(command.ExecuteScalar());

Answer 4

I'm using Oracle. If your sql returns numeric value, which is int, you need to use Convert.ToInt32(object). Here is the example below:

public int GetUsersCount(int userId)
{
    using (var conn = new OracleConnection(...)){
        conn.Open();
        using(var command = conn.CreateCommand()){
            command.CommandText = "select count(*) from users where userid = :userId";
            command.AddParameter(":userId", userId);            
            var rowCount = command.ExecuteScalar();
            return rowCount == null ? 0 : Convert.ToInt32(rowCount);
        }
    }
}

Answer 5

I had this issue when the user connecting to the database had CONNECT permissions, but no permissions to read from the database. In my case, I could not even do something like this:

object userNameObj = command.ExecuteScalar()

Putting this in a try/catch (which you should probably be doing anyway) was the only way I could see to handle the insufficient permission issue.

Answer 6

In your case either the record doesn't exist with the userid=2 or it may contain a null value in first column, because if no value is found for the query result used in SQL command, ExecuteScalar() returns null.