c# multiple dropdowns

Table i need to sort

So i got this 5 drop downs i need to use for sorting output from sql

Now i use

DropDownList_Instruktorer.Items.Insert(0, new ListItem("Vælg Instruktør", "*"));

For the Default Value, and i was thinking this will do the job. But

cmd.Parameters.addwithvalue

enter the value into value obviously instead of use * to show all results like it normally does in sql

SqlCommand cmd = new SqlCommand(@"SELECT * FROM Hold 
                                            INNER JOIN Instruktorer
                                            ON instruktor_id = fk_in_id
                                            INNER JOIN Stilarter
                                            ON stilart_id = fk_st_id
                                            INNER JOIN  Aldersgruppe
                                            ON aldersgruppe_id = fk_ag_id
                                            INNER JOIN Niveauer
                                            ON niveau_id = fk_ni_id
                                            INNER JOIN Tider
                                            ON tid_id = fk_ht_id
                                            WHERE fk_in_id = @Instruktor AND
                                            fk_st_id = @Stilart AND
                                            fk_ag_id = @Aldersgruppe AND
                                            fk_ni_id = @Niveau AND
                                            fk_ht_id = @Tid", conn);
    cmd.Parameters.AddWithValue("@Instruktor", DropDownList_Instruktorer.SelectedValue);
    cmd.Parameters.AddWithValue("@Stilart", DropDownList_Stilart.SelectedValue);
    cmd.Parameters.AddWithValue("@Aldersgruppe", DropDownList_Aldersgrupper.SelectedValue);
    cmd.Parameters.AddWithValue("@Niveau", DropDownList_Niveauer.SelectedValue);
    cmd.Parameters.AddWithValue("@Tid", DropDownList_Tider.SelectedValue);

Here is my sql, Any idea how i can i get it to work without writing 25 if statements?