How Do I Delete From A Table

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hey , i want to delete a selected "staff member" (displayed in listbox) / my code

C#

private void button2_Click(object sender, EventArgs e)
        {
            SqlConnection con = new SqlConnection("Data Source=JAMES-PC\\SQLEXPRESS;Initial Catalog=staff;Integrated Security=True");
            con.Open();

            string sql = @"DELETE FROM staff1 where Id=@name;";

            SqlCommand cmd = new SqlCommand(sql, con);
            cmd.Parameters.AddWithValue("@name", 1);

            cmd.ExecuteNonQuery();
            con.Close();
        }

but when i run the program i click the button (remove) but no luck, doesnt delete it
any help would be appreciated
also the table displayed in the listbox is (name)

Posted 5-Aug-15 22:46pm

jamesmc1535

Updated 5-Aug-15 22:53pm

Suvendu Shekhar Giri

v2

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Comments

Suvendu Shekhar Giri 6-Aug-15 4:55am

but you have hardcoded value for Id to be 1, is it for a purpose?

jamesmc1535 6-Aug-15 5:00am

my friend helped me out with the code and he said i should add that part,so no i didnt insert that part i jus followed advice? / is it needed? how would i know if its needed?

Arasappan 6-Aug-15 5:11am

put a break point on the open { and run the proram

jamesmc1535 6-Aug-15 5:21am

did that,ran the program , got error ? must declare a scalar variable @name

Arasappan 6-Aug-15 5:27am

can u please show ur table and parameters

Arasappan 6-Aug-15 5:28am

example
staff_id bigint;
staff_name nvarchar(10);

jamesmc1535 6-Aug-15 6:14am

okay my table names are ass follows
name / surname / homead / location / position / cellnum / email listbox uses (name)
they all are varchar(50)

Arasappan 6-Aug-15 6:18am

u write in query id=@name please change that where id=@id what about the id on ur table..

jamesmc1535 6-Aug-15 6:22am

i hate sql :D uhm im goin to tell you how i made my table /
started query > create database staff1
use staff1

>create table name(
id primary key identity < is that hat you were refering to ?

Arasappan 6-Aug-15 6:26am

simply write where id=@id

jamesmc1535 6-Aug-15 6:29am

okay my code looks like this now >
SqlConnection con = new SqlConnection("Data Source=JAMES-PC\\SQLEXPRESS;Initial Catalog=staff;Integrated Security=True");
con.Open();

string sql = @"DELETE FROM staff1 where Id=@id;";

SqlCommand cmd = new SqlCommand(sql, con);
cmd.Parameters.AddWithValue("@id", listBox1.SelectedItem.ToString());

cmd.ExecuteNonQuery();
con.Close();<pre>
but i still get this error >
Conversion failed when converting the nvarchar value 'michsafj' to data type int.

Arasappan 6-Aug-15 6:33am

try this
string sql = @"DELETE FROM staff1 where name=@name;";

jamesmc1535 6-Aug-15 6:35am

Must declare the scalar variable "@name"
lol XD

jamesmc1535 6-Aug-15 6:36am

nevermind fixed it it worked i changed it 2 that but forgot to change
cmd.Parameters.AddWithValue("@id", listBox1.SelectedItem.ToString());
to
cmd.Parameters.AddWithValue("@name", listBox1.SelectedItem.ToString());

Arasappan 6-Aug-15 6:37am

what is your table name,I thing ur not including name column on that

jamesmc1535 6-Aug-15 6:40am

just another small follow up question>when i click delete it deletes but i have to close the form and reopen it again for the listbox to update is there a way to make it able to auto update so when i click remove its removed from the listbox instantly?

Arasappan 6-Aug-15 6:42am

now are u clear with deletion.

jamesmc1535 6-Aug-15 6:44am

yes its working now thanks

Arasappan 6-Aug-15 6:56am

Always moving to delete by means of id so only we use primary key identity,Because it may chance two name of james in the table..

jamesmc1535 6-Aug-15 7:01am

oh thanks man now it makes more sense :) because i wondered what that was so now u cleared that up :)

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Arasappan · Accepted Answer · 2015-08-05T23:23:00

Go to Web Config and paste this

XML

<connectionStrings>
    <add name="constring" connectionString="data source=JAMES-PC\\SQLEXPRESS; initial catalog=staff; persist security info= true; integrated security= true" providerName="System.Data.SqlClient"/>
  </connectionStrings>

and chane the code as follow

private void button2_Click(object sender, EventArgs e)
        {
            SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["constring"].ConnectionString);
            con.Open();
 
            string sql = @"DELETE FROM staff1 where name=@name;";
 
            SqlCommand cmd = new SqlCommand("DELETE FROM staff1 where name=@name", con);
            cmd.Parameters.AddWithValue("@name", 1); or  //cmd.Parameters.AddWithValue("@name", listBox1.SelectedItem.ToString());
 
            cmd.ExecuteNonQuery();
            con.Close();
        }

Always go with id for deletion.Thank You:-)

sreeyush sudhakaran · Accepted Answer · 2015-08-05T23:21:00

Solution 1

C#

private void button2_Click(object sender, EventArgs e)
{
            SqlConnection con = new SqlConnection("Data Source=JAMES-PC\\SQLEXPRESS;Initial Catalog=staff;Integrated Security=True");
            con.Open();
 
            string sql = @"DELETE FROM staff1 where Id=@name;";
 
            SqlCommand cmd = new SqlCommand(sql, con);
            cmd.Parameters.AddWithValue("@name", listBox1.SelectedValue.ToString());
 
            cmd.ExecuteNonQuery();
            con.Close();
}

see if the parameter id is varchar it is enclosed like this:
DELETE FROM staff1 where Id= 'staff1';

Posted 5-Aug-15 23:21pm

sreeyush sudhakaran

Updated 5-Aug-15 23:38pm

v4

Comments

jamesmc1535 6-Aug-15 5:26am

Conversion failed when converting the nvarchar value 'james' to data type int. get a error

sreeyush sudhakaran 6-Aug-15 5:32am

that means you need the id not staff name in the place , for that select both id , staff name from database and then set :
listBox1.DisplayMember = "staffname";//Name of the field as in Database
listBox1.ValueMember = "id";//Name of the field as in Database
listBox1.DataSource = Ds; // A Datasource filled by Querying the database

Arasappan 6-Aug-15 5:31am

cmd.Parameters.AddWithValue("@name", int.Parse(listBox1.SelectedItem.ToString()));
or
cmd.Parameters.AddWithValue("@name", listBox1.SelectedValue.ToString());