Decimal Floating-Point Types

SQL Language StructureCommon Language Elements

Decimal Floating-Point Types

Decimal floating-point values are stored in an IEEE 754 decimal format that comprises sign, exponent and coefficient.Contrary to the approximate floating-point data types, precision is either 16 or 34 decimal digits.

`DECFLOAT`

Data Type Declaration Format

DECFLOAT [(dec_prec)]

Table 1. `DECFLOAT` Type Parameters
Parameter	Description
dec_prec	Precision in decimal digits, either 16 or 34.Default is 34.

DECFLOAT is a SQL standard-compliant numeric type that stores floating-point number precisely (decimal floating-point type), unlike FLOAT or DOUBLE PRECISION that provide a binary approximation of the purported precision.

The type is stored and transmitted as IEEE 754 standard types Decimal64 (DECFLOAT(16)) or Decimal128 (DECFLOAT(34)).

All intermediate calculations are performed with 34-digit values.

16-digit and 34-digit

The “16” and “34” refer to the maximum precision in Base-10 digits.See https://en/wikipedia.org/wiki/iEEE_754#Basic_and_interchange_formats for a comprehensive table.

Table 2. Range of Values
Type	Maximum precision	Minimum Exponent	Maximum Exponent	Smallest value	Largest value
`DECFLOAT(16)`	16	-383	+384	1E-398	9.9..9E+384
`DECFLOAT(34)`	34	-6143	+6144	1E-6176	9.9..9E+6144

Observe that although the smallest exponent for DECFLOAT(16) is -383, the smallest value has an exponent of -398, but 15 fewer digits.And similar for DECFLOAT(34), smallest exponent is -6143, but the smallest value has an exponent of -6176, but 33 fewer digits.The reason is that precision was “sacrificed” to be able to store a smaller value.

This is a result of how the value is stored: as a decimal value of 16 or 34 digits and an exponent.For example, 1.234567890123456e-383 is stored as coefficient 1234567890123456 and exponent -398, while 1E-398 is stored as coefficient 1, exponent -398.