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[SOLVED] variables for money


M.O.S. Studios

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For simple actions this is fine the better way is to actually use the money_format function( http://us.php.net/money_format)

and to treat the values as floats not integers.  which means to use them as floats in your database with precision of 2

 

There isn't such a thing as a 'float with a precision of 2'. What you mean is probably a numeric/decimal type.

See SQL antipatterns presentation available in mysql forums here on phpfreaks to see the difference between the two.

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Then it's not a float anymore, because float, as its name implies has floating point (and variable precision).

 

But this is technical discussion about how types are implemented.

 

Let's have an example, that shows how float and decimal types differ in practice.

 

First a table

CREATE TABLE  `floatvsdecimal` (
  `ID` int(10) unsigned NOT NULL auto_increment,
  `fl` float NOT NULL default '0',
  `decm` decimal(5,2) NOT NULL default '0.00',
  PRIMARY KEY  (`ID`)
);

 

Then data:

insert 1000 rows like this one.

INSERT INTO `floatsvsdecimal` VALUES
(null,0.33,0.33);

 

And now select:

 

SELECT sum(`fl`), sum(`decm`) FROM floatvsdecimal;

 

Results:

+-----------------+-----------+
| sum(fl)         | sum(decm) |
+-----------------+-----------+
| 330.00001311302 |    330.00 | 
+-----------------+-----------+

 

1000 rows, and there's a discrepancy on fifth decimal place. You need 1'000'000 rows for it to show up in second decimal place. If the values inserted into a table were more varied as in real life, it's possible that the discrepancy was even larger (or smaller). What's more, it can vary between hardware platforms and operating systems.

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