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Hidden Rounding
Many versions of SQL support a Decimal data type. Microsoft SQL Server, in particular, allows the user to specify the total number of digits as well as the number of decimal places a particular variable or column supports.
The ability to define the number of decimals and decimal places is valuable because you can optimize the amount of space required by narrowing the data type to only the precision you require.
This is where hidden rounding comes into place. When working with an MS SQL Server data type such as Money, or Small Money, you know what the precision is based on the specific data type. In contrast, when you work with a decimal data type, you have to look at the metadata of the table or definition of a variable in order to know the true precision of the data contained.
Because of implicit conversion, when mixing different decimal data types, some operations round the more precise variable implicitly to the lower precision definition. Without an understanding of the precision of all data types involved, rounding may be implicitly happening, and not apparent to the programmer.
The rounding may not be a bad, or undesirable thing. However, if it is not apparent that rounding is occurring, there can be unexpected consequences.
How do you use Decimal data types in your SQL Schemas? Do you prefer to use other data types? If you do use decimals, do you have best practices you have found useful? Share your thoughts with us by sending your Email to btaylor@sswug.org.
Cheers,
Ben
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