Re: MySQL function in a Table's Column

From: Date: Sat, 24 Nov 2001 23:54:49 +0000
Subject: Re: MySQL function in a Table's Column
References: 1  Groups: php.general 
Request: Send a blank email to php-general+get-75625@lists.php.net to get a copy of this message
> I basically want to make a column that will do math to other columns, like in > a spreadsheet program. Is it possible? And if so, what do I look for? > And if you can give me an example that would be great. No, you can't do that, you store the raw data, and do the math when you retrieve it. It's bad database design to store summary data (i.e. a total order amount vs calculating from detail lines), or data that can be derived within a row itself by caclulating from other fields. The reasons are basically that it wastes space in the db, and that the calculated values become out of balance (and require cleanup programs/scripts to realign them). Sometimes one must store this type of info for efficiency purposes, and in those cases, the value is calculated (by you) and then stored in the db; but it should be avoided as much as possible because of the db integrity issue noted above. In a spreadsheet it's different, right, the value isn't stored, it's calculated when the sheet is modified. That's what you need to do. Retrieve the row, calculate the value in the script, and display it. It looks to the end-user like it was in the db, but only the basic info is there, such as qty, and unit price. The extended price is calculated on demand as needed from those two basic entities.

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