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Hi
smallmoney type takes up to 4 bytes. Monetary data values from 214,748.3648 through +214,748.3647, with accuracy to a tenthousandth of a monetary unit.
Yet decimal(9,4) takes 5 bytes (as I understand it) yet doesn't store as large a range.
decimal(9,4) can only store 21474.3647 but use one more byte




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So...what's your question?
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2 datatypes, one can store more digits in less bytes than the other, I must of missed something obvious here..
I'm asking as I wanted to use decimal (9,3) for prices, yet smallmoney uses one less byte and can store bigger numbers.




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Then the short answer is, use the variable with the smallest footprint that meets your requirements: in this case, smallmoney.
As to the onebyte difference, I can't say definitively as I haven't researched it, but I'd say it has something to do with the need for the decimal type to have varying scale, whereas money and smallmoney are fixed at scale = 4. Research BOL for "datatypes" for more info.
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Decimal(9,3) can store 999,999.999 to 999,999.999 Decimal(9,4) is 99,999.9999 to 99,999.9999
Not sure, but I think they're stored differently internally  decimal as an integer* with a factor of 10 multiplier, money as a standard integer. E.g. in decimal(9,4), 12345.6789 is stored as 123456789 x 10^4 *(Integer here means the mathematical definition, not the datatype).
As precision increases, the bytes needed to store the integer increase to accommodate the maximum possible value.
4 bytes is enough to store 999,999,999 but not 9,999,999,999 Perhaps the extra byte stores the factor of 10 to multiply by?
For smallmoney, you'll notice the maximum value of a 4byte integer is 2,147,483,647, which equals 214,748.3647 x 10^4, the maximum value of smallmoney. Don't need to store the factor of 10 multiplier as it's always 4 in smallmoney.




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terry999 (9/25/2012)
smallmoney type takes up to 4 bytes decimal(9,4) can only store 21474.3647 but use one more byte The ranges of the two types have been discussed already, but there is another consideration:
 Result is $1.0000 typed as smallmoney DECLARE @credit smallmoney = $1.99; SELECT @credit / 10000 * 10000; GO  Result is 1.9900000000 typed as decimal (21, 10) DECLARE @credit decimal(9,4) = 1.99; SELECT @credit / 10000 * 10000;
This may or may not be important to you, but the characteristics of the data type might be more interesting than saving a byte here or there. Indeed, there may be no byte to save if row compression is active, or if the extra byte per row does not result in at least one row having to be stored on a separate data page.
Paul White SQLPerformance.com SQLblog.com @SQL_Kiwi




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... The ranges of the two types have been discussed already, but there is another consideration:  Result is $1.0000 typed as smallmoney DECLARE @credit smallmoney = $1.99; SELECT @credit / 10000 * 10000; GO  Result is 1.9900000000 typed as decimal (21, 10) DECLARE @credit decimal(9,4) = 1.99; SELECT @credit / 10000 * 10000;
...
In the above example by Paul White, you can see where the rounding happens and how it can potentially cause issues. So, If you work with monetary datatypes you should understand how SQL works with them and when rounding is performed. Try this one:
 Result is $1.99 typed as smallmoney DECLARE @credit smallmoney = $1.99; SELECT @credit * 10000 / 10000;
The reason it works fine for decimal is that SQL converts result of decimal(9,4) division by integer to decimal(21,10)
Check this one:
SELECT 1.99 / 10000.00 SELECT 1.99 / 10000.0 SELECT 1.99 / 10000 SELECT 1.9900 / 10000.00 SELECT 1.9900 / 10000.0 SELECT 1.9900 / 10000
So, I do prefer working with decimals as there are less thing to worry about, but sometimes you stuck with what you have. So, you should know implications and ways around.
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Eugene Elutin (9/26/2012) If you work with monetary datatypes you should understand how SQL works with them and when rounding is performed. Are you talking to me?
Paul White SQLPerformance.com SQLblog.com @SQL_Kiwi




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SQL Kiwi (9/26/2012)
Eugene Elutin (9/26/2012) If you work with monetary datatypes you should understand how SQL works with them and when rounding is performed.Are you talking to me?
No! Sorry, I was not explicit enough. My post addressed to OP.
Please check if my edit did make a change...
_____________________________________________ "The only true wisdom is in knowing you know nothing" "O skol'ko nam otkrytiy chudnyh prevnosit microsofta duh!" (So many miracle inventions provided by MS to us...)
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