PHP MySQL - Storing Configuration Then Reffering To The Config By Date

I'm building an Insurance Site, and will be selling policies online.

I'm designing the database at the minute and need 开发者_JS百科some advice on the best way to store the rates I'm using to calculate the premium.

There's a clever way of selecting the rates, based on the date the policy was purchased - from a rates table, using like an 'effective date' field or something.

Has anyone done this? I'm struggling to find examples. I know what i'm trying to achieve just not how to build the tables to do it.

Order the rates table by the date effective and pick the first.

SELECT * FROM Rates
  WHERE effective > ?
  OREDR BY effective 
  LIMIT 1

This will return the first (lowest) date for which the rate is effective.

PS: The ? is where your date goes.