执行第一个命令后，我将如何执行另一个SELECT命令？

Question

protected void Button1_Click(object sender, EventArgs e) 
    { 
     string client = TextBox1.Text; 
     string selected = RadioButtonList1.SelectedValue; 
     string calendar = Calendar1.SelectedDate.ToShortDateString(); 
     string disease = txtDisease.Text; 

     SqlCommand insert = new SqlCommand("insert into Appointment(Client_ID, DateofAppointment, TimeofAppointment, Disease) values(@Client_ID, @DateofAppointment, @TimeofAppointment, @Disease)", conn); 
     try 
     { 
      conn.Open(); 

      SqlCommand cmd = new SqlCommand("select * from Client where Client_ID = @Client_ID", conn); 
      cmd.Parameters.AddWithValue("@Client_ID", TextBox1.Text); 
      SqlDataAdapter da = new SqlDataAdapter(cmd); 
      DataTable dt = new DataTable(); 
      da.Fill(dt); 
      if (dt.Rows.Count > 0) 
      {  
        insert.Parameters.AddWithValue("@Client_ID", client); 
        insert.Parameters.AddWithValue("@DateofAppointment", calendar); 
        insert.Parameters.AddWithValue("@TimeofAppointment", selected); 
        insert.Parameters.AddWithValue("@Disease", disease); 
        insert.ExecuteNonQuery(); 
        TextBox1.Text = ""; 
        RadioButtonList1.SelectedIndex = -1; 
        txtDisease.Text = ""; 
        ClientScript.RegisterStartupScript(Page.GetType(), "validation", "<script language='javascript'>alert('Appointment submitted! Please wait for your SMS confirmation. Thank you!')</script>"); 
      } 
      else 
      { 
       TextBox1.Text = ""; 
       RadioButtonList1.SelectedIndex = -1; 
       txtDisease.Text = ""; 
       ClientScript.RegisterStartupScript(Page.GetType(), "validation", "<script language='javascript'>alert('You are not a registered client!')</script>"); 
      } 
     } 
     catch 
     { 
      conn.Close(); 
     } 

    } 


} 

我想创建另一个命令来搜索日期和领带是否已经被插入到我的数据库之前。

Answer 1

不确定你最初的例外情况是什么，但在发布问题时加入该例外很有帮助。

另外关于您的连接，通常不推荐使用级别连接。 Sql Server为你处理连接池，所以最好的做法是在你完成使用后立即处理你的连接。当你想重新查询（在另一个方法或类中），然后创建一个新的连接。同时将您的连接包裹在using区块中，以确保它们关闭并丢弃。

而关于你的日期，最好始终坚持原生类型的数据。这意味着您的日期的列类型应该是Sql日期，而不是字符串。这也意味着您的日历参数值应为DateTime calendar = Calendar1.SelectedDate;而不是string。

protected void Button1_Click(object sender, EventArgs e) 
{ 
    string client = TextBox1.Text; 
    string selected = RadioButtonList1.SelectedValue; 

    // this should be a DateTime instance, not a string 
    string calendar = Calendar1.SelectedDate.ToShortDateString(); 

    string disease = txtDisease.Text; 

    try 
    { 
     conn.Open(); 

     SqlCommand cmd = new SqlCommand("select 1 from Appointment WHERE DateofAppointment = @DateofAppointment AND TimeofAppointment = @TimeofAppointment", conn); 
     cmd.Parameters.AddWithValue("@DateofAppointment", calendar); 
     cmd.Parameters.AddWithValue("@TimeofAppointment", selected); 
     bool exists = false; 
     using(var reader = cmd.ExecuteReader()) { 
      exists = reader.Read(); // if this returns true there is a record 
     } 

     // do something based on exists 

     SqlCommand insert = new SqlCommand("insert into Appointment(Client_ID, DateofAppointment, TimeofAppointment, Disease) values(@Client_ID, @DateofAppointment, @TimeofAppointment, @Disease)", conn); 

     // repurpose same pointer but to different instance 
     cmd = new SqlCommand("select * from Client where Client_ID = @Client_ID", conn); 
     cmd.Parameters.AddWithValue("@Client_ID", TextBox1.Text); 
     SqlDataAdapter da = new SqlDataAdapter(cmd); 
     DataTable dt = new DataTable(); 
     da.Fill(dt); 
     if (dt.Rows.Count > 0) 
     {  
       insert.Parameters.AddWithValue("@Client_ID", client); 
       insert.Parameters.AddWithValue("@DateofAppointment", calendar); 
       insert.Parameters.AddWithValue("@TimeofAppointment", selected); 
       insert.Parameters.AddWithValue("@Disease", disease); 
       insert.ExecuteNonQuery(); 
       TextBox1.Text = ""; 
       RadioButtonList1.SelectedIndex = -1; 
       txtDisease.Text = ""; 
       ClientScript.RegisterStartupScript(Page.GetType(), "validation", "<script language='javascript'>alert('Appointment submitted! Please wait for your SMS confirmation. Thank you!')</script>"); 
     } 
     else 
     { 
      TextBox1.Text = ""; 
      RadioButtonList1.SelectedIndex = -1; 
      txtDisease.Text = ""; 
      ClientScript.RegisterStartupScript(Page.GetType(), "validation", "<script language='javascript'>alert('You are not a registered client!')</script>"); 
     } 
    } 
    catch 
    { 
     conn.Close(); 
    } 
} 

Answer 2

您可以在第一个之前创建的命令并执行第二前检查结果：

cmd.CommandText = "SELECT COUNT(*) FROM Client where {you conditions}"; 
Int32 count = (Int32) cmd.ExecuteScalar(); 

，然后检查count大于0，则执行第二。

Answer 3

保护无效Button1_Click（对象发件人，EventArgs e） { string client = TextBox1.Text; string selected = RadioButtonList1.SelectedValue; string calendar = Calendar1.SelectedDate.ToShortDateString（）; string disease = txtDisease.Text;

 SqlCommand insert = new SqlCommand("insert into Appointment(Client_ID, DateofAppointment, TimeofAppointment, Disease) values(@Client_ID, @DateofAppointment, @TimeofAppointment, @Disease)", conn); 
     try 
     { 
      conn.Open(); 

      SqlCommand cmd = new SqlCommand("select * from Client where Client_ID = @Client_ID", conn); 
      cmd.Parameters.AddWithValue("@Client_ID", TextBox1.Text); 
      SqlDataAdapter da = new SqlDataAdapter(cmd); 
      DataTable dt = new DataTable(); 
      da.Fill(dt); 
      if (dt.Rows.Count > 0) 
      { 
       SqlCommand search = new SqlCommand("select * from Appointment where DateofAppointment = @DateofAppointment and TimeofAppointment = @TimeofAppointment", conn); 
       search.Parameters.AddWithValue("@DateofAppointment", calendar); 
       search.Parameters.AddWithValue("@TimeofAppointment", selected); 
       Int32 count = (Int32)search.ExecuteScalar(); 
       if (count > 0) 
       { 
        ClientScript.RegisterStartupScript(Page.GetType(), "validation", "<script language='javascript'>alert('Error!')</script>"); 
       } 
       else 
       { 
        insert.Parameters.AddWithValue("@Client_ID", client); 
        insert.Parameters.AddWithValue("@DateofAppointment", calendar); 
        insert.Parameters.AddWithValue("@TimeofAppointment", selected); 
        insert.Parameters.AddWithValue("@Disease", disease); 
        insert.ExecuteNonQuery(); 
        TextBox1.Text = ""; 
        RadioButtonList1.SelectedIndex = -1; 
        txtDisease.Text = ""; 
        ClientScript.RegisterStartupScript(Page.GetType(), "validation", "<script language='javascript'>alert('Appointment submitted! Please wait for your SMS confirmation. Thank you!')</script>"); 
       } 
      } 
      else 
      { 
       TextBox1.Text = ""; 
       RadioButtonList1.SelectedIndex = -1; 
       txtDisease.Text = ""; 
       ClientScript.RegisterStartupScript(Page.GetType(), "validation", "<script language='javascript'>alert('You are not a registered client!')</script>"); 
      } 
     } 
     catch 
     { 
      conn.Close(); 
     } 

    } 


} 

它仍然没有工作... :(