SQL Server : UPDATE Relation Table

Question

I want to update my relation table between book and user named R_Kital_Al But I get this error ;

System.Data.SqlClient.SqlException (0x80131904): Cannot insert duplicate key row in object 'dbo.R_Kitap_Al' with unique index 'IX_Kitap_Al'. The duplicate key value is (15).

How can I fix this error?

private void Update_Click(object sender, EventArgs e)
{
        SqlConnection conn = new SqlConnection(@"Data Source=HP\SQLEXPRESS;Initial Catalog=Kütüphane;Integrated Security=True");

        conn.Open();
        SqlCommand cmd = new SqlCommand("UPDATE R_Kitap_Al SET SSN=@SSN,Book_No=@Book_No,BaslamaTarihi=@BaslamaTarihi,BitisTarihi=@BitisTarihi", conn);
        DateTime dt = new DateTime();
        cmd.Parameters.AddWithValue("@SSN",dataGridView1.CurrentRow.Cells[0].Value);
        cmd.Parameters.AddWithValue("@Book_No",book_NoTextBox.Text);
        cmd.Parameters.AddWithValue("@BaslamaTarihi",baslamaTarihiDateTimePicker.Value);
        dt = Convert.ToDateTime(baslamaTarihiDateTimePicker.Value);
        dt = dt.AddDays(0);
        bitisTarihiDateTimePicker.Value = dt.AddDays(15);
        cmd.Parameters.AddWithValue("@BitisTarihi", bitisTarihiDateTimePicker.Value);

        cmd.ExecuteNonQuery();
        this.Hide();
        R_Kitap_Al kit = new R_Kitap_Al();
        kit.ShowDialog();
        this.Close();
}

Answer 1

There is no where clause so you are updating every row in that table with the specified values. Is one of those columns a primary or foreign key?

Answer 2

We cannot insert duplicate value in unique Unique Key.

So, In your table 'SSN' or 'Book_No ' column might be Unique. Please check '15' exists in column 'SSN' or 'Book_No'

Please remove unique key from mention column or try to update with different value rather than 15.