I want to ask you how to fill combo box using c# and in sql server

string connecttionstring = System.Configuration.ConfigurationManager.ConnectionStrings["connectionString"].ConnectionString;
            SqlConnection cs1 = new SqlConnection(connecttionstring);
            SqlCommand cmd1 = new SqlCommand();
            cs1.Open();
            cmd1.CommandText = "your select Query";
            cmd1.Connection = cs1;
            DataSet dtst = new DataSet();
            SqlDataAdapter dp = new SqlDataAdapter(cmd1);
            dp.Fill(dtst);// for select query
            DropDownList1.DataSource = dtst;
            DropDownList1.DataTextField = "Value you want to show";//this value should be there in your select query
            DropDownList1.DataValueField = "Value you want to select ";//this value should be there in your select query
            DropDownList1.DataBind();

see Populate data from database in a ComboBox[^]

try this

SqlCommand cmd = new SqlCommand("yourquery", yourConnection);
           SqlDataReader dr = cmd.ExecuteReader();

while (dr.Read())
            {
                comboBox1.Items.Add(dr[Index].ToString());
            }
            dr.Close();

and

private void BindComboBox()
{
  comboBox1.DataSource = dataSet1.Tables["TableName"];
  comboBox1.DisplayMember = "ColumnName";
}

Take a look there-[Bind a Windows Forms ComboBox or ListBox Control to Data][^] for details.

My sql server Table is:-
User_Id Name
1 Prince
2 Rakesh
3 Rahul

Now my table name is Student

-----
In C# Windows application:-
Declare the page load event

SqlConnection con = new SqlConnection(//Connection string);
      SqlDataAdapter     adpter = new SqlDataAdapter("Select * from cUser", con);
           DataSet ds = new DataSet();
           adpter.Fill(ds);
           comboBox1.DataSource = ds.Tables[0];
           comboBox1.DisplayMember = "Name";
           comboBox1.ValueMember = "User_Id";

In above solution ComboBox1 is my combobox


In another way of you use go to combobox and choose the datasource property and add project data source

now you select the displaymember property for which you want to display. also ValueMamber property use for display value.

3rd Method

SqlConnection con = new SqlConnection(//Connection string);
       SqlDataAdapter     adpter = new SqlDataAdapter("Select * from cUser", con);
            DataSet ds = new DataSet();
            adpter.Fill(ds);
           for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
            {
                comboBox1.Items.Add(ds.Tables[0].Rows[i][0].ToString());
            }

public void fill_groups()
        {

            try
            {
                sqlConnection  con = new sqlConnection (connectionstring);
                DataSet ds = new DataSet();
                sqlDataAdapter  ad = new sqlDataAdapter ("select  groupname from groupNames ", con);
                ad.Fill(ds);
                cmbgroup.Items.Add("---Select---");
                for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
                {
                    cmbgroup.Items.Add(ds.Tables[0].Rows[i][0].ToString());

                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
          
        }

SqlCommand cmd = new SqlCommand("yourquery", yourConnection);
           SqlDataReader dr = cmd.ExecuteReader();
 
while (dr.Read())
            {
                comboBox1.Items.Add(dr.Getstring(0).ToString());
            }
            dr.Close();

Hi,
C# - Populate a ComboBox with data from a DataTable[^]