代碼為：Commandstr = "INSERT INTO t_user (code, idcard, name) values("+TextBox1.Text+","+TextBox2.Text+","+TextBox3.Text+")";SqlConnection myConnection = new SqlConnection("Server=localhost\\SQLEXPRESS;database=student;uid=;pwd=;Integrated Security=true");myConnection.Open(); SqlCommand myCommand = new SqlCommand(Commandstr, myConnection);myCommand.ExecuteNonQuery();myConnection.Close();表為：ID INT CODE NCHAR(10)IDCARD NCHAR(10)NAME NCHAR(10)其中ID已經設為主鍵，標識種子，標識增量都已經設為1，但一運行就出現“不能將值 NULL 插入列 'id'，表 'student.dbo.t_user'；列不允許有空值。INSERT 失敗。語句已終止。 ”這是什么原因？應該如何改那應該怎么改呢？具體一點……