dupicate username validation

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i have created 2 pages login and password.and i am checking for duplicate entry of username.
i have written query for it.But how can prevent it from inserting if the username is same.i have tried further but it is wrong.pls help
here is my code-

C#

 protected void signupbtn_Click(object sender, EventArgs e)
    {
        try
        {
            conn.Open();
        string st;
            st = "select count(username)from login where username='" + txtname.Text + "'";
            cmd = new SqlCommand(st, conn);
            if (st > 0)
            {
                Response.Write("duplicate record");
            }
         else
{
 cmd = new SqlCommand("insert into login(name,midname,surname,username,password,contact,dob,email,address,occupation,ltype) values('" + txtfirst.Text + "','" + txtmid.Text + "','" + txtsur.Text + "','" + txtname.Text + "','" + txtpass.Text + "','" + txtcontact.Text + "','" + txtdob.Text + "','" + txtemail.Text + "','" + txtaddr.Text + "','" + txtocc.Text + "','" + typeButtonList1.SelectedValue + "')", conn);


                cmd.ExecuteNonQuery();
                Response.Write("Record inserted");
            }
        }

Posted 17-Jan-14 3:11am

Member 10523130

Updated 17-Jan-14 3:14am

Karthik_Mahalingam

v2

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Karthik_Mahalingam · Answer 1 · 2014-01-17T03:18:00

Solution 1

Be aware of SQL_injection[^] as it is not safe to frame the query in c#..

try like this..

C#

conn.Open();
           string st;
           st = "select count(username)from login where username='" + txtname.Text + "'";
           var cmd = new SqlCommand(st, conn);
           DataTable dt = new DataTable();
           SqlDataAdapter da = new SqlDataAdapter(cmd);
           da.Fill(dt);
           int count = Convert.ToInt32(dt.Rows[0][0]);
           if (count >= 1)
           {
               Response.Write("duplicate record");
           }

Posted 17-Jan-14 3:18am

Karthik_Mahalingam

Updated 17-Jan-14 3:24am

v4

Comments

Member 10523130 17-Jan-14 9:27am

It is not working.. I think my if statement is wrong..??

Karthik_Mahalingam 17-Jan-14 9:30am

did u check this code ??
your if statement is compile error, invalid statements...

Member 10523130 17-Jan-14 9:34am

yes it is giving error..but how can check if that count is not 0??

Karthik_Mahalingam 17-Jan-14 9:35am

what error ?

( count != 0 )

Member 10523130 17-Jan-14 9:41am

ok..I have not included using system.data(). it is not giving error but it is not working also

Member 10523130 17-Jan-14 9:45am

hey thanx it worked

Karthik_Mahalingam 17-Jan-14 9:57am

if your issue is solved. pls close this post...

Member 10523130 17-Jan-14 9:47am

i have one more query related to sql databse..i have set primary key id to auto increment..bt after 8 record it shows id 1069..why is it so?

Karthik_Mahalingam 17-Jan-14 9:59am

Can you post an new question.. as we are moving out of the Topic...
so that many people who are expert in sql can give u a right solution...
:)

Maciej Los · Answer 2 · 2014-01-17T06:12:00

First of all, have you ever heard about SQL injection[^]? An ASP.NET application should be created in that way which provide protection of sql injection attacks[^].

I strongly recommend to use stored procedures and call it from code behind[^]. If you would like to avoid logins duplication, set this field as unique[^]!
How to: Creating and Modifying UNIQUE Constraints[^]