why this code insert duplicate rows with different id

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C#

Hi,

this is my function to insert new row

public int addrow(string sqlcommand)
        {
            int res = 0;
            try
            {
                con.Open();
                cmd.CommandText = sqlcommand;
                cmd.Connection = con;
                cmd.ExecuteNonQuery();
                if (cmd.ExecuteNonQuery() == 1)
                    res = 1;
            }
            catch (Exception exp)
            {
                throw exp;
            }

            finally
            {
                con.Close();
            }
            return res;
        }

when i call this function it inserted twice rows

string command = "insert into caseT values(N'" + caseTxt.Text + "')";
            int addRow = db.addrow(command);
            if (addRow == 1)
            {
                MessageBox.Show("inserted");
                caseTxt.Text = "";
                fillCase();
            }

1 case1
2 case2

any help