How should I create unique bill/account numbers?

What do you people use for generating unique account numbers? Some use Autoinc field, others something else... What would be the prope开发者_运维技巧r way i.e to get an account number before I run the insert query?

---

If you are using a SQL database, use a Generator. If you want to use an independent mechanism you could consider using a GUID.

---

You haven't told us what database system you are using, but from the sound of it, you're talking about the Paradox tables in Delphi. If so, an autoInc column can work, although if I recall correctly, you have to be very careful when moving your data around with Paradox autoInc columns because they re-generate from zero when moved.

As has been mentioned, you can use GUIDs - sysutils.function CreateGUID(out Guid: TGUID): HResult; - they will always be unique, but the downside in GUIDS is that ordering by these keys will not be intuitive and probably be meaningless, so you'll need a timestamp column of some sort to maintain the order of your inserts, which can be important. Also, a GUID is a rather long character string and will not be very efficient for use as an account#, which assumedly will be a primary or foreign key in many tables.

So I'd stick to autoInc if you want something automatic, but if you have to move data around and you need to maintain your original keys, load your original autoincs as integer columns in their new location or you could end up corrupting your entire database. (I believe there are other scenarios that also cause autoIncs to reset in Paradox tables - research this if it's relevant - been a long time since I've used Pdox, and it may not be a problem with other flat file databases)

If you are indeed using a database server - SQLServer, Oracle, Interbase, etc, they all have autoInc/indentity or generator functionality, sometimes in conjuction with a trigger - that is your best option.

Dorin's answer is also an excellent solution if you want to handle this yourself from within your Delphi code. Create a global, thread safe function to implement it - that will ensure a very high level of safety.

HTH

---

Depending on how long you want the number, you can go with Jamies MD5 conversion or:

var
  LDateTime: TDateTime;
  LBytes: array[0..7] of Byte absolute LDateTime;
  LAccNo: string;
  Index: Integer;
begin
  LDateTime := Now;
  LAccNo := EmptyStr;
  for Index := 0 to 7 do
    LAccNo := LAccNo + IntToHex( LBytes[ Index ], 2 );
  // now you have a code in LAccNo, use it wisely (:
end;

---

I use this PHP snippet to generate a decent account number:

$account_number = str_replace(array("0","O"),"D",strtoupper(substr(md5(time()),0,7)));

This will create a 7 digit varchar string that doesn't contain 0's or o's (to avoid errors on the phone or transcribing them in e-mails, etc.) You get something like EDB6DA6 or 76337D5 or DB2E624.