Why All Of The Records Are Updating When I Updating One Record Why?

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C#

SQL-Server

SQL-Server-2008

, +

my code is

protected void btnupdate_Click(object sender, EventArgs e)
{
try
{
SqlConnection con = new SqlConnection(cs);
SqlCommand cmd = new SqlCommand("update Employee1 set EmployeeName=@PEmployeeId,EmployeeDesignation=@PEmployeeDesignation,EmployeeDOJ=@PEmployeeDOJ,EmployeeSalary=@PEmployeeSalary,EMployeeDepartmentno=@PEmployeeDepartmentno", con);
cmd.CommandType = CommandType.Text;
cmd.Parameters.AddWithValue("@PEmployeeId", TextBox1.Text);
cmd.Parameters.AddWithValue("@PEmployeeName", TextBox2.Text);
cmd.Parameters.AddWithValue("@PEmployeeDesignation", TextBox3.Text);
cmd.Parameters.AddWithValue("@PEmployeeDOJ", TextBox4.Text);
cmd.Parameters.AddWithValue("@PEmployeeSalary", TextBox5.Text);
cmd.Parameters.AddWithValue("@PEmployeeDepartmentno", TextBox6.Text);
con.Open();
int i = cmd.ExecuteNonQuery();
con.Close();
Console.WriteLine("Data Updated");
}
catch (Exception ex)
{

lblmessage.Text = ex.Message;
}
The Records which are in my table all of them are updating when i updating one record form my table