Personal finance app database design -

after searching around minimalistic money tracking/budgeting app, decided build 1 own personal use.

however i'm unsure part of database design. @ moment, have entries table stores data each transaction, whether credit or debt etc.

the dilemma have is, don't know if should create table store current balance of each account or if should populate dynamically subtracting debits credits.

part of me saying entries table grows ability generate balance each account slower (yes premature optimization supposedly evil), seems unnecessary add table when can calculate data existing tables.

thanks

edit: sorry may not have been clear, understand how implement either method of creating account balance. more looking advantages/disadvantages of either method 'best practice'. replies!

if design minimalistic accounting application, 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 consist of date , zero-padded numeric value (i.e. 201102230000) last 4 digits daily transaction id. useful track transactions , return range, etc. daily transaction id 0000 account balance @ beginning (or end) of day, , id 0001 , other transactions.

the column trans_type hold transaction codes, such "deb" (debit), "cre" (credit), "tra" (transfer) , "bal" (balance), etc.

with setup that, can perform kind query, getting "credit" transactions between given date, account balance @ given date, or date range.

example: fetch credit , debit transactions between 2011-01-01 , 2011-02-23

select ledger.*, account.name, category.name   ledger   join account     on ledger.account_id = account.account_id   join category     on ledger.category_id = category.category_id  (ledger.trans_type = "cre"      or ledger.trans_type = "deb")    , ledger.key between 201101010000 , 201102239999  order ledger.key asc 

example: fetch transactions (except balances) between 2011-01-01 , 2011-02-23 account #1 (ex: mortgage)

select ledger.*, account.name, category.name   ledger   join account     on ledger.account_id = account.account_id   join category     on ledger.category_id = category.category_id  ledger.trans_type <> "bal"    , ledger.key between 201101010000 , 201102239999    , account.id = 1  order ledger.key asc 

so there go, flexibility , extensibility.