asp.net 防止用户重复注册

[tianxiongfei]

怎样防止用户名重复注册啊 这是我写的 但一直提示有错误
请高手帮我看看怎么写？（注册页面：用户名-textbox1,密码-textbox2,密码确认--textbox3,邮箱--textbox4）


protected void Button1_Click(object sender, EventArgs e)
{
String sjkxm=TextBox1.Text;
SqlConnection conn = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\news.mdf;Integrated Security=True;User Instance=True");
conn.Open();
SqlCommand cmd = new SqlCommand("select count(*) from [user] where username=" + sjkxm, conn);
int s=Int32.Parse(cmd.ExecuteScalar().ToString());
if (s==0)
{
Console.WriteLine("用户名重复");
}
if (s==1)
{
register.registeruser(TextBox1.Text, TextBox2.Text, TextBox4.Text,'0');
Label1.Visible = true;
Label1.Text = "恭喜你注册成功";
}

}

[智者知已应修善业]

用户名称检查数据库有无即可

[[̲̅孤̲̅单̲̅一̲̅吻̲̅]]

以前ASP的，给你个参考
sql="select * from iymm where username='" &usernamea &"'"
rs.open sql,db,3,2
if not rs.eof then
response.write "<script>window.alert('您欲注册的昵称已经存在');history.back(-1);</script>"
response.end
end if

[dys_198102]

看看。顶一下

[MicrosoftCenterOfHN]

SqlCommand cmd = new SqlCommand("select count(*) from [user] where username=" + sjkxm, conn);
修改为:
SqlCommand cmd = new SqlCommand("select count(*) from [user] where username='" + sjkxm+"'", conn);

[open_boy]

数据库加约束就行了

[wjn161]

简单的办法，加一个按钮“检查用户名是否重复”
麻烦一点的办法,用ajax自动提示~
至于代码.google搜一下，足够用了