3下拉列表搜索功能

我是c#的新手，如.

我目前正在c#中使用3个DropDownLists和一个提交按钮进行搜索。当用户在DropDownList上选择一个项目并单击提交时，它将打印相应选择的表格。

有3个下拉列表：

1. 一个省
2. 城市
3. 专业化

这将搜索适合选择的可用医生。例如，我在第一个下拉列表上选择省1，在第二个下拉列表中选择城市1，并在第三个下拉列表选择心理学家，当按下提交按钮时，它将打印省1、城市1中有心理学家专业知识的可用医生。

我已经有了一个代码，还在想，但当我点击提交按钮时，什么都没有发生。有人能帮我吗？

以下是我迄今为止所做的：

public partial class Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        System.Threading.Thread.Sleep(1000);
        if (!IsPostBack)
        {
            string constring = ConfigurationManager.ConnectionStrings["AccreString"].ConnectionString;
            SqlConnection conn = new SqlConnection(constring);
            DataTable dt = new DataTable("emed_province");
            using (conn)
            {
                conn.Open();
                SqlCommand comm = new SqlCommand("SELECT * FROM emed_province ORDER BY PROVINCE_NAME ASC", conn);
                SqlDataAdapter adptr = new SqlDataAdapter(comm);
                adptr.Fill(dt);
            }
            ddlProvince.DataSource = dt;
            ddlProvince.DataTextField = "PROVINCE_NAME";
            ddlProvince.DataValueField = "PROVINCE_CODE";
            ddlProvince.DataBind();
            ddlProvince.Items.Insert(0, new ListItem("---------------SELECT---------------", "0"));
            ddlCity.Items.Insert(0, new ListItem("---------------SELECT---------------", "0"));
            ddlSpec.Items.Insert(0, new ListItem("---------------SELECT---------------", "0"));
        }
    }
    protected void ddlProvince_SelectedIndexChanged(object sender, EventArgs e)
    {
        System.Threading.Thread.Sleep(1000);
        string constring = ConfigurationManager.ConnectionStrings["AccreString"].ConnectionString;
        SqlConnection conn = new SqlConnection(constring);
        DataTable dt = new DataTable("emed_province");
        using (conn)
        {
            conn.Open();
            SqlCommand comm = new SqlCommand("SELECT * FROM emed_city WHERE PROVINCE_CODE =@pcode", conn);
            comm.Parameters.AddWithValue("@pcode", ddlProvince.SelectedValue);
            SqlDataAdapter adptr = new SqlDataAdapter(comm);
            adptr.Fill(dt);
            SqlParameter param = new SqlParameter();
            param.ParameterName = "@pcode";
            param.Value = ddlProvince;
            comm.Parameters.Add(param);
        }
        ddlCity.DataSource = dt;
        ddlCity.DataTextField = "CITY_NAME";
        ddlCity.DataValueField = "CITY_CODE";
        ddlCity.DataBind();
        ddlCity.Items.Insert(0, new ListItem("---------------SELECT---------------", "0"));
    }
    protected void ddlCity_SelectedIndexChanged(object sender, EventArgs e)
    {
        System.Threading.Thread.Sleep(1000);
        string constring = ConfigurationManager.ConnectionStrings["AccreString"].ConnectionString;
        SqlConnection conn = new SqlConnection(constring);
        DataTable dt = new DataTable("emed_city");
        using (conn)
        {
            conn.Open();
            SqlCommand comm = new SqlCommand("SELECT * FROM emed_specialization", conn);
            comm.Parameters.AddWithValue("@ccode", ddlCity.SelectedValue);
            SqlDataAdapter adptr = new SqlDataAdapter(comm);
            adptr.Fill(dt);
            SqlParameter param = new SqlParameter();
            param.ParameterName = "@ccode";
            param.Value = ddlCity;
            comm.Parameters.Add(param);
        }
        ddlSpec.DataSource = dt;
        ddlSpec.DataTextField = "SPEC_NAME";
        ddlSpec.DataValueField = "SPEC_CODE";
        ddlSpec.DataBind();
        ddlSpec.Items.Insert(0, new ListItem("---------------SELECT---------------", "0"));
    }
    protected void btnSub_Click(object sender, EventArgs e)
    {
        string constring = ConfigurationManager.ConnectionStrings["AccreString"].ConnectionString;
        SqlConnection conn = new SqlConnection(constring);
        DataTable dt = new DataTable("emed_doctors");
        using (conn)
        {
            conn.Open();
            SqlCommand comm = new SqlCommand("SELECT DOCTOR_NAME FROM emed_doctors where Province = '" + ddlProvince.SelectedItem.ToString() + "'", conn);
            SqlDataAdapter adptr = new SqlDataAdapter(comm);
            adptr.Fill(dt);
        }
    }
}

SqlCommand comm = new SqlCommand("SELECT DOCTOR_NAME FROM emed_doctors where province = '" + ddlProvince.SelectedItem.ToString() + "'", conn); 

SqlCommand comm = new SqlCommand("SELECT DOCTOR_NAME FROM emed_doctors where (" + ddlProvince.SelectedItem.ToString() + " ", conn);