Richard Huxton wrote:
Okay, this simple example really exists, but the simple table also includes a date that the stock was last traded, so we have:Ron St-Pierre wrote:
Richard Huxton wrote:
An "update or insert" would be useful sometimes, but it's not always necessary. Indeed, if I find I don't know whether I'm adding or updating something I take a long hard look at my design - it ususally means I've not thought clearly about something.
Can you give an actual example of where you need this?
How about stocks for a simple example? Let's say you have a simple table with the stock symbol, stock exchange, high, low, open, close and volume. Every day you update the data for each stock. But there are always new stocks listed on an exchange, so when a new stock shows up you have to do an insert instead of an update.
If it is just a simple table then delete all of them and insert from scratch. If you wanted to track changes over time (perhaps more likely), you'd have a separate table with the company name/address etc and a log table. At which point you'll want to know if it's a new company or not...
stock symbol, stock exchange, high, low, open, close, volume, date, plus a few more fields
But the data isn't always updated at one time, as we can update all stocks for one exhange and possibly only some of the stocks for a particular exchange in one go. Even if the data is received for only one exchange we could delete all stocks for that exchange and insert new ones, which would work fine. However some stocks are not traded every day, so we need to show the trading information for the last date that it was traded, so we can't delete them en masse even for the one exchange.
BTW these updates do take longer than we'd like so I would appreciate more input on how this setup could be redesigned.
Ron
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