如何通过使用SQL查询将所有列值（已应用不同的值）检索到列表框中？

Question

This might be simple one and also this has been answered before but I don't know how to look for the exact method.

-> Am having two list box in my form. One is for product name and other one is for Company name.

-> On page load, Listbox1 will retrieve values from database(Product name) . Once item has been selected from listbox1 , the respective company names should be fetched in listbox2 .

For eg : Database name is Motor

Here is my table named as "Register" and it contains two columns they are,

Productname        Companyname

Car                 Bmw
Bike                Bmw
Car                 Honda
Bike                Honda

My Question is

I retrieved product name details into listbox1 , here the thing is i don't want to repeat the same items, so I used Distinct like this,

Select Distinct Productname from Register

Now if i select car from listbox 1 then the respective company names should be display in listbox2. But what am getting is only Honda on my listbox2 and am not getting BMW.

Sqlcommand cmd=new Sqlcommand("Select Companyname from Register where Productname='"+listbox1.selecteditem+"'",con);
Sqldatareader dr=cmd.Executereader();
while(dr.Read())
{
   string a=dr.GetString(0);
   listbox2.items.add(a);
}

This is the query which is used to retrieve values into listbox2. I used datareader to read and get the values from the database.

I don't know exactly how to do this. Hope am not confusing you.So any help would be more helpful to me and thanks in advance.

Answer 1

Have you tried with,

    Select Companyname from Register 
    where Productname='"+listbox1.GetItemText(listbox1.SelectedItem)+"'

Answer 2

Try this..

Sqlcommand cmd=new Sqlcommand("Select Companyname from Register where Productname='"+listbox1.selecteditem.toString()+"'",con);
Sqldatareader dr=cmd.Executereader();

listbox2.items.clear();

while(dr.Read())
{
   string a=dr['Companyname'].toString();
   listbox2.items.add(a);
}

Answer 3

ur using string a=dr.GetString(0); listbox2.items.add(a);

which will fetch only first row from table..

use string a=dr["companyname"].toString(); listbox2.items.add(a);

this should solve your problem.