Microsoft SQL Server 中的小数数据类型

From MSDN:

float and real

Approximate number data types for use with floating point numeric data. Floating point data is approximate; not all values in the data type range can be precisely represented.

Syntax

float [ ( n ) ]

Is a floating point number data with the following valid values: - 1.79E + 308 through -2.23E - 308, 0 and 2.23E -308 through 1.79E + 308. n is the number of bits used to store the mantissa of the float number in scientific notation and thus dictates the precision and storage size. n must be a value from 1 through 53. The default value of n is 53.

n is	Precision	Storage size
1-24	7 digits	4 bytes
25-53	15 digits	8 bytes

The Microsoft® SQL Server™ float[(n)] data type conforms to the SQL-92 standard for all values of n from 1 to 53. The synonym for double precision is float(53).

real

Is a floating point number data with the following valid values: –3.40E + 38 through -1.18E - 38, 0 and 1.18E - 38 through 3.40E + 38. Storage size is 4 bytes. In SQL Server, the synonym for real is float(24).

Note  Microsoft® SQL Server™ 2000 treats n as one of two possible values. If 1<=n<=24,  n is treated as 24. If 25<=n<=53, n is treated as 53.

decimal and numeric (Transact-SQL)

Numeric data types that have fixed precision and scale.

decimal[ (p[ , s] )] and numeric[ (p[ , s] )]

Fixed precision and scale numbers. When maximum precision is used, valid values are from - 10^38 +1 through 10^38 - 1. The ISO synonyms for decimal are dec and dec(p, s). numeric is functionally equivalent to decimal.

p (precision)

The maximum total number of decimal digits that can be stored, both to the left and to the right of the decimal point. The precision must be a value from 1 through the maximum precision of 38. The default precision is 18.

s (scale)

The maximum number of decimal digits that can be stored to the right of the decimal point. Scale must be a value from 0 through p. Scale can be specified only if precision is specified. The default scale is 0; therefore, 0 <= s <= p. Maximum storage sizes vary, based on the precision.

Precision	Storage bytes
1 - 9	5
10-19	9
20-28	13
29-38	17

money and smallmoney (Transact-SQL)

Data types that represent monetary or currency values.

Data type	Range	Storage
money	-922,337,203,685,477.5808 to 922,337,203,685,477.5807	8 bytes
smallmoney	- 214,748.3648 to 214,748.3647	4 bytes