If not exists???

if you want to do in database you no need to check in C#
just do 

IF(NOT EXISTS(select * from table))

        BEGIN        
                DO SOMETING
        END
ELSE
        BEGIN
        //DO SOMETING
        END

After such a long time... finally it worked... M happy  

OK.... PLEASE MARK THE ANSWER AS ACCEPTED IF MY ANSWERS HAVE HELPED YOU

Thank you.

OK

Try writing your own Select and Insert Statements with the same logic I have used.... I have written it with respect to Ms-Sql Server...

It is giving the error because I have not written proper statement. So you try writing your own Select and Insert Script with the same logic I have applied and check it....

Best thing is, that you first write and test the scripts in the MySql Server first... If it works fine, then copy and paste it in your code...

I have added MySQL.Data.dll v2.0

Errors:

command.CommandText = "Select 1 from test where ID = '" + trade.OtherSID + "'"";
Reader = command.ExecuteReader();

-> unexepted Symbol ';'



command.CommandText = "Insert into test(id) Values('" + trade.OtherSID + "'" )";
                                         Reader.Close();

-> unexepted Symbol ')' exepting ';' or '}'

I hope you have added the MySql Dll as a reference in your application... If you have added it, then use these following namespaces...

using System;
using MySql.Data;
using MySql.Data.MySqlClient;

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Thank you.

thank you a lot...
But I think i have to write using ... on the top?
What kind of using... to i need?

Do you have TeamViewer?
Than you can edit it, how you want and you can see the errors...

Hey meinenr, Try this out...

Thank you!

string myInsertQuery = "INSERT INTO test (id) Values ('"+trade.OtherSID+"')"; //here it must ask if the enrtie "trade.OtherSID" already exist in the column.


Can you please write the little part for me:

if the value of the trade.OtherSID already exists you can write:

//nothing happens
or
PrintConsole("ALREADY EXIST!!", ConsoleColor.Red);

else (if the value of the trade.OtherSID does not exist) you can write:

//add it
or
string myInsertQuery = "INSERT INTO test (id) Values ('"+trade.OtherSID+"')";

So you want to check that the "trade.OtherSID" already exists in the test table, right???
What do you want to do if the value of the trade.OtherSID alread exists???

I already Connect to a Databease:


string myConnectionString = "SERVER=localhost;" +
        "DATABASE=test;" +
          "UID=root;" +
          "PASSWORD=;";
     
      MySqlConnection connection = new MySqlConnection(myConnectionString);
      MySqlCommand command = connection.CreateCommand();
      command.CommandText = "SELECT * FROM test";
      MySqlDataReader Reader;
      connection.Open();
      Reader = command.ExecuteReader();
      while (Reader.Read())
      {
        string row = "";
        for (int i = 0; i < Reader.FieldCount; i++)
          row += Reader.GetValue(i).ToString() + ", ";
        Console.WriteLine(row);
      }
      connection.Close();
      if(myConnectionString == "")
      {
        myConnectionString = "Database=test;Data Source=localhost;User Id=root;Password=";
      }

      MySqlConnection myConnection = new MySqlConnection(myConnectionString);
       
      string myInsertQuery = "INSERT INTO test (id) Values ('"+trade.OtherSID+"')"; //here it must ask if the enrtie "trade.OtherSID" already exist in the column.

      MySqlCommand myCommand = new MySqlCommand(myInsertQuery);
      myCommand.Connection = myConnection;
      myConnection.Open();
      myCommand.ExecuteNonQuery();
      myCommand.Connection.Close();

Absolutely you will have to add the MySql Dll reference in your project.... Just check out the link that I have mentioned... It is for connecting to MySql database using Visual Studio 2008 or 2010....

But you can still try out!!!

OK you are using MySql database for storing your data... No problem, then you do not have to add the namespaces "using System.Data" and "using System.Data.SqlClient".

These namespaces are usually used to work with MS-SQL Database...

Check out this link, on how to connect to MySql Database, how to insert data and how to get data from the table....
http://www.codeproject.com/Tips/423233/How-to-Connect-to-MySQL-Using-Csharp

Hope this helps you.

I have create a C# Consele Project.
I use MonoDevelop.
It will me a Bot soon.
I already used "using MySql.Data.MySqlClient", but there I have to install MySQL.data.dll and add it as referenc.

Firstly tell me, what kind of an application are you developing???
and are you creating a C# ASP.NET Application or a Website or a C# Console Application???

Which technology are you using to create your application?

The mentioned namespaces are usually used in .Net applications while connecting to the MS-SQL Server. 

using System.Data and System.Data.SqlClient gives us pre-defined classes like "SqlConnection", "SqlCommand", Datasets, "SqlDataAdapters", "SqlDataReaders" and many others.....

To access a MS-SQL Database, you have to use these namespaces.

I have Problems whith this lines:

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

I have to add some reference to use them?

I used already the following lines:
using System;
using System.Collections.Generic;
using System.Linq;
using SteamKit2;
using MySql.Data.MySqlClient;

The  trade.OtherSID  holds that value right??? So I am checking that value in the Select Query...
"Select testName from test where testID = '" + trade.OtherSID +"'");"

This Query will return me the testName if it founds the ID from your table matching with the trade.OtherSID value. The "testName" in the above query is just an example to select some value from the table....

Complete Explanation of the above script


1. First I am creating a Sql Connection Object and adding the Connection String as a Parameter.
SqlConnection con = new SqlConnection("Connection String"); 

2. Then I am opening the Connection
con.Open();

3. Then I am creating a SQL Command Object passing a Select query with the " trade.OtherSID " to check its ID with the ID in the test Table.
SqlCommand cmd = new SqlCommand("Select testName from test where testID = '" + trade.OtherSID +"'");

4. Then I creating a Sql DataReader Object to read values which we get from the Select Query.
SqlDataReader dr = null;
dr = cmd.ExecuteReader();
while (dr.Read())
{
5. While reading the values from the DataReader, I am just checking if the reader object contains the value returned by the Select Statement
if(!String.IsNullOrEmpty(dr[0].ToString()))
{
 Console.WriteLine(dr[0].ToString()); // Print If the reader has a value at its zero'th position
}
else
{
 Console.WriteLine("Test Name Does Not Exist");
} 
}

If you are creating a web application, then you will have to use the mentioned Namespaces otherwise for a Console Application use the following...

using System;

using System.Data;

using System.Data.SqlClient;

Sorry, but i don't understannd your script.

Where is the line, which check if the ID (STEAM:1:0:XXXX....) exist in the column in my table?


I need to use all of this:
using System;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Data.SqlClient;

Ok I thought, you just want to check if there is any value in the trade.OtherSID.... For the question you have mentioned, you will have to do something like this....


Example: 
Your Table name: test
Columns in your table "test"


testID testName
STEAM:1:0:XXXX        test123xyz...
STEAM:2:0:wxyz         test456abc...


Suppose you want to get the TestName from the table and check whether the "STEAM:1:0:XXXX" ID exists in your table, you will have to do the following...


using System;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Data.SqlClient;


public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
    }


    protected void btnLogin_Click(object sender, EventArgs e)
    {
        if (!String.IsNullOrEmpty(trade.OtherSID))
        {
            SqlConnection con = new SqlConnection("Connection String");// Setting the Connection with the SQL Database


            con.Open();// Opening the Connection


   // Create a Command Object and pass the Select query to get the field based on the trade.OtherSID
            SqlCommand cmd = new SqlCommand("Select testName from test where testID = '" + trade.OtherSID +"'");




   SqlDataReader dr = null;
            dr = cmd.ExecuteReader();// Execute the Reader and get the value in the DataReader Object
            while (dr.Read())// Read the values from the DataReader object until all the values are being read.
            {
if(!String.IsNullOrEmpty(dr[0].ToString())); // Since there is only 1 value being achieved in the Datareader Object, Check if it is null or empty
{
Console.WriteLine(dr[0].ToString()); // Print If the reader has a value at its zero'th position
}
else
{
Console.WriteLine("Test Name Does Not Exist");// Print this if the reader object does not contain any value
}
   }
   con.Close(); // Close the Connection after completing the Transaction with the Data Source.
        }
    }
}


Hope this helps you out....
Let me know if you have any doubt!!!7

MARK THE ANSWER AS ACCEPTED IF IT HELPED YOU

Thank you,
but if (!String.IsNullOrEmpty( trade.OtherSID )) ask if trade.OtherSID is "0" or "", but trade.OtherSID ist aways STEAM:1:0:XXXX....

I wanted to check if the entrie STEAM:1:0:XXXX.... exist in the column 'id' in my databe table 'test'.

Hey meinenr, For inserting the value you can write something like this.... The below written example is with MS-SQL Database...

using System;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Data.SqlClient;

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
    }


    protected void btnLogin_Click(object sender, EventArgs e)
    {
// trade.OtherSID should return a String Value  otherwise you will have to use Convert.ToString(trade.OtherSID)

        if (!String.IsNullOrEmpty( trade.OtherSID ))        {
            SqlConnection con = new SqlConnection("Connection String");
            con.Open();
            SqlCommand cmd = new SqlCommand("Insert into test (id)" + "Values(" + trade.OtherSID  +")");
            cmd.ExecuteNonQuery(); // Returns an integer value
 con.Close();
        }
    }
}
This is just a sample example....
HOPE THIS HELPS YOU....

How does it work for:
string myInsertQuery = "INSERT INTO test (id) Values ('"+trade.OtherSID+"')";

How i can check if this entrie (trade.OtherSID) already exist?

Hey if its a string value, then you can take the value in the string and check it with the IsNullOrEmpty() method of the String Object....

eg: 
string Value = "Some value will come here";
if(!String.IsNullOrEmpty(Value))
{
        Console.WriteLine(Value);
}
else
{
        Console.WriteLine("Nothing Exists");
}