Appropriate datatype for holding percent values?

Question

What is the best datatype for holding percent values ranging from 0.00% to 100.00%?

Answer 1

• Hold as a decimal.
• Add check constraints if you want to limit the range (e.g. between 0 to 100%; in some cases there may be valid reasons to go beyond 100% or potentially even into the negatives).
• Treat value 1 as 100%, 0.5 as 50%, etc. This will allow any math operations to function as expected (i.e. as opposed to using value 100 as 100%).
• Amend precision and scale as required (these are the two values in brackets columnName decimal(precision, scale). Precision says the total number of digits that can be held in the number, scale says how many of those are after the decimal place, so decimal(3,2) is a number which can be represented as #.##; decimal(5,3) would be ##.###.
• decimal and numeric are essentially the same thing. However decimal is ANSI compliant, so always use that unless told otherwise (e.g. by your company's coding standards).

Example Scenarios

• For your case (0.00% to 100.00%) you'd want decimal(5,4).
• For the most common case (0% to 100%) you'd want decimal(3,2).
• In both of the above, the check constraints would be the same

Example:

if object_id('Demo') is null
create table Demo
    (
        Id bigint not null identity(1,1) constraint pk_Demo primary key
        , Name nvarchar(256) not null constraint uk_Demo unique 
        , SomePercentValue decimal(3,2) constraint chk_Demo_SomePercentValue check (SomePercentValue between 0 and 1)
        , SomePrecisionPercentValue decimal(5,2) constraint chk_Demo_SomePrecisionPercentValue check (SomePrecisionPercentValue between 0 and 1)
    )

Further Reading:

• Decimal Scale & Precision: http://msdn.microsoft.com/en-us/library/aa258832%28SQL.80%29.aspx
• 0 to 1 vs 0 to 100: C#: Storing percentages, 50 or 0.50?
• Decimal vs Numeric: Is there any difference between DECIMAL and NUMERIC in SQL Server?