SQL Server: Calculation with numeric literals
floating-point, precision, sql-server-2005
Solution
SQL Server uses the smallest possible datatype.
When you run this script
SELECT SQL_VARIANT_PROPERTY(1.0, 'BaseType')
SELECT SQL_VARIANT_PROPERTY(1.0, 'Precision')
SELECT SQL_VARIANT_PROPERTY(1.0, 'Scale')
SELECT SQL_VARIANT_PROPERTY(1.0, 'TotalBytes')
you'll see that SQL Server implicitly used a NUMERIC(2, 1) datatype. The division by 60.0 converts the result to NUMERIC(8, 6). The final calculation converts the result to NUMERIC(17, 10).
Edit
Taken from SQL Server Books Online Data Type Conversion
In Transact-SQL statements, a constant with a decimal point is automatically converted into a numeric data value, using the minimum precision and scale necessary. For example, the constant 12.345 is converted into a numeric value with a precision of 5 and a scale of 3.
Problem
I did some testing with floating point calculations to minimize the precision loss. I stumbled across a phenomen I want to show here and hopefully get an explanation. When I write ``` print 1.0 / (1.0 / 60.0) ``` the result is ``` 60.0024000960 ``` When I write the same formula and do explicit casting to `float` ``` print cast(1.0 as float) / (cast(1.0 as float) / cast(60.0 as float)) ``` the result is ``` 60 ``` Until now I thought that numeric literals with decimal places are automatically treated as `float` values with the appropriate precision. Casting to `real` shows the same result as casting to `float`. - Is there some documentation on how SQL Server evaluates numeric literals? - Of what datatype are those literals? - Do I really have to cast them to `float` get better precision (which sounds like irony to me :)? - Is there an easier way than cluttering my formulas with casts?