Get The Value From SELECT Query From A Table?

how to get the value from SELECT query from a table

protected void Button_Click(object sender, EventArgs e)
{
string select_qry = "SELECT ID, USER, FILE, DATE, LASTUSED from FILE_INFO where USER = '" + user + "'"; // ID is primary key
SqlCommand cmd = new SqlCommand(select_qry);
GridView1.DataSource = GetData(cmd);
GridView1.DataBind();
}
private DataTable GetData(SqlCommand cmd)
{
DataTable dt = new DataTable();
SqlDataAdapter sda = new SqlDataAdapter();
cmd.CommandType = CommandType.Text;
cmd.Connection = conn1;
conn1.Open();
sda.SelectCommand = cmd;
sda.Fill(dt);
return dt;
}

I have different USERS I want to get ID of user if user is different say 'Sheena' has ID value from 1-10 but if user is 'Sara' and she is having ID from 11-20 so I want to get specially ID of particular user how do I get ID from select query can any one know)