3.2. FloatingPoint Data Types
Firebird supports two types of floatingpoint data types: approximate or binary floatingpoint data types (FLOAT
and DOUBLE PRECISION
), and decimal floatingpoint types (DECFLOAT
).
3.2.1. Approximate FloatingPoint Data Types
Approximate floatingpoint data types are stored in an IEEE 754 binary format that comprises sign, exponent and mantissa.
Precision is dynamic, corresponding to the physical storage format of the value, which is exactly 4 bytes for the FLOAT
type and 8 bytes for DOUBLE PRECISION
.
Considering the peculiarities of storing floatingpoint numbers in a database, these data types are not recommended for storing monetary data. For the same reasons, columns with floatingpoint data are not recommended for use as keys or to have uniqueness constraints applied to them.
For testing data in columns with floatingpoint data types, expressions should check using a range, for instance, BETWEEN
, rather than searching for exact matches.
When using these data types in expressions, extreme care is advised regarding the rounding of evaluation results.
3.2.1.1. FLOAT
Data Type Declaration Format
FLOAT [(bin_prec)]
FLOAT
Type ParametersParameter  Description 

bin_prec  Precision in binary digits, default is 24 1  24: 32bit single precision 25  53: 64bit double precision 
The FLOAT
data type defaults to a 32bit single precision floatingpoint type with an approximate precision of 7 decimal digits after the decimal point (24 binary digits).
To ensure the safety of storage, rely on 6 decimal digits of precision.
The syntax FLOAT(bin_prec)
was introduced in Firebird 4.0, and behaves as follows:
1 <= _bin_prec <= 23: 32bit single precision (synonym for
FLOAT
)25 <= _bin_prec <= 53: 64bit double precision (synonym for
DOUBLE PRECISION
)
The behaviour of FLOAT
(without explicit precision) behaves as the SQL standard type Section 3.2.1.2, “REAL
”.
Firebird 3.0 and earlier supported
FLOAT(dec_prec)
where dec_prec was the approximate precision in decimal digits, with 0 <= dec_prec <= 7 mapped to 32bit single precision and P > 7 mapped to 64bit double precision. This syntax was never documented.For bin_prec in
FLOAT(bin_prec)
, the values 1 <= bin_prec <= 24 are all treated as bin_prec = 24, values 25 <= bin_prec <= 53 are all handled as bin_prec = 53.Most Firebird tools will report
FLOAT(1)
FLOAT(24)
asFLOAT
, andFLOAT(25)
FLOAT(53)
asDOUBLE PRECISION
.
3.2.1.2. REAL
Data Type Declaration Format
REAL
The data type REAL
is a synonym for FLOAT
, and is provided for syntax compatibility.
When used to define a column or parameter, it’s indistinguishable from using FLOAT
or FLOAT(1)
 FLOAT(24)
.
REAL
has been available as a synonym forFLOAT
since Firebird 1.0 and even earlier, but was never documented.Most Firebird tools will report
FLOAT
forREAL
.
3.2.1.3. DOUBLE PRECISION
Data Type Declaration Format
DOUBLE PRECISION
The DOUBLE PRECISION
data type is stored with an approximate precision of 15 digits.
Firebird also has the — previously undocumented — synonyms for
DOUBLE PRECISION
:LONG FLOAT
andLONG FLOAT(bin_prec)
, with 1 <= bin_prec <= 53.These nonstandard type names are deprecated and may be removed in a future Firebird version.
Firebird 3.0 and earlier supported
LONG FLOAT(dec_prec)
where dec_prec was the approximate precision in decimal digits, where any value for dec_prec mapped to 64bit double precision.
3.2.2. Decimal FloatingPoint Types
Decimal floatingpoint are stored in an IEEE 754 decimal format that comprises sign, exponent and coefficient. Contrary to the approximate floatingpoint data types, precision is either 16 or 34 decimal digits.
3.2.2.1. DECFLOAT
Data Type Declaration Format
DECFLOAT [(precision)]
DECFLOAT
Type ParametersParameter  Description 

precision  Precision in decimal digits, either 16 or 34. Default is 34. 
DECFLOAT
is a SQL:2016 standardcomplient numeric type that stores floatingpoint number precisely (decimal floatingpoint 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 34digit values.
Type  Maximum precision  Minimum Exponent  Maximum Exponent  Smallest value  Largest value 

 16  383  +384  1E398  9.9..9E+384 
 34  6143  +6144  1E6176  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 smalles 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 1.234567890123456e383
is actually stored as coefficient 1234567890123456
and exponent 398
, while 1E398
is stored as coefficient 1
, exponent 398
.
3.2.2.1.1. Behaviour of DECFLOAT
Operations
The behaviour of DECFLOAT
operations in a session, specifically rounding and error behaviour, can be configured using the SET DECFLOAT
management statement.
3.2.2.1.2. Length of DECFLOAT
Literals
It is possible to express DECFLOAT(34)
values in approximate numeric literals, but only for values with a mantissa of 20 or more digits, or an absolute exponent larger than 308.
Scientific notation literals with fewer digits or a smaller absolute exponent are DOUBLE PRECISION
literals.
Exact numeric literals with 40 or more digits — actually 39 digits, when larger than the maximum INT128
value — are also handled as DECFLOAT(34)
.
Alternatively, use a string literal and explicitly cast to the desired DECFLOAT
type.
The length of DECFLOAT
literals cannot exceed 1024 characters.
Scientific notation is required for greater values.
For example, 0.0<1020 zeroes>11
cannot be used as a literal, the equivalent in scientific notation, 1.1E1022
is valid.
Similarly, 10<1022 zeroes>0
can be presented as 1.0E1024
.
Literals with more than 34 significant digits are rounded using the DECFLOAT
rounding mode of the session.
3.2.2.1.3. DECFLOAT
and Functions
Use with Standard Functions
A number of standard scalar functions can be used with expressions and values of the DECFLOAT
type.
They are:










The aggregate functions SUM
, AVG
, MAX
and MIN
work with DECFLOAT
data, as do all the statistics aggregates (including but not limited to STDDEV
or CORR
).
Special Functions for DECFLOAT
Firebird supports four functions, designed to support DECFLOAT
data specifically:
COMPARE_DECFLOAT
compares two
DECFLOAT
values to be equal, different or unorderedNORMALIZE_DECFLOAT
takes a single
DECFLOAT
argument and returns it in its simplest formQUANTIZE
takes two
DECFLOAT
arguments and returns the first argument scaled using the second value as a patternTOTALORDER
performs an exact comparison on two
DECFLOAT
values
Detailed descriptions are available in the Special Functions for DECFLOAT
section of the Builtin Scalar Functions chapter.