Personal finance app database design

Question

After searching around for a minimalistic money tracking/budgeting app, I decided to build one for my own personal use.

However I\'m unsure with part of the database

Answer 1

If I were to design a minimalistic accounting application, I would probably do something like

ledger
-------------
   key          INT(12) PRIMARY KEY
   account_id   INT(10)
   category_id  INT(10)
   trans_type   CHAR(3)
   amount       NUMERIC(10,2)

account
------------
   account_id   INT(10) PRIMARY KEY
   created      DATETIME
   name         VARCHAR(32)
   ...

category
------------
   category_id  INT(10)
   name         VARCHAR(32)
   ...

The column key would consist of a date and a zero-padded numeric value (i.e. 201102230000) where the last 4 digits would be the daily transaction id. This would be useful to track the transactions and return a range, etc. The daily transaction id 0000 could be the account balance at the beginning (or end) of the day, and the id 0001 and up are other transactions.

The column trans_type would hold transaction codes, such as "DEB" (debit), "CRE" (credit), "TRA" (transfer) and "BAL" (balance), etc.

With a setup like that, you can perform any kind a query, from getting all the "credit" transactions between any given date, to only the account balance at any given date, or date range.

Example: fetch all credit and debit transactions between 2011-01-01 and 2011-02-23

SELECT ledger.*, account.name, category.name
  FROM ledger
  JOIN account
    ON ledger.account_id = account.account_id
  JOIN category
    ON ledger.category_id = category.category_id
 WHERE (ledger.trans_type = "CRE"
     OR ledger.trans_type = "DEB")
   AND ledger.key BETWEEN 201101010000 AND 201102239999
 ORDER BY ledger.key ASC

Example: fetch all transactions (except balances) between 2011-01-01 and 2011-02-23 for the account #1 (ex: Mortgage)

SELECT ledger.*, account.name, category.name
  FROM ledger
  JOIN account
    ON ledger.account_id = account.account_id
  JOIN category
    ON ledger.category_id = category.category_id
 WHERE ledger.trans_type <> "BAL"
   AND ledger.key BETWEEN 201101010000 AND 201102239999
   AND account.id = 1
 ORDER BY ledger.key ASC

So there you go, flexibility and extensibility.