Numeric types consist of two-, four-, and eight-byte integers, as well as eight-byte floating-point numbers and selectable-precision decimals. Table 1.2 lists the available types.
Table 1.2. Numeric Types
| Name | Storage Size | Description | Range |
|---|---|---|---|
smallint | 2 bytes | small-range integer | -32768 to +32767 |
integer | 4 bytes | typical choice for integer | -2147483648 to +2147483647 |
bigint | 8 bytes | large-range integer | -9223372036854775808 to +9223372036854775807 |
numeric | 8 or 16 bytes | exact, fixed-length representation of numbers with decimal point | up to 38 digits |
double precision | 8 bytes | variable-precision, inexact | 15 decimal digits precision |
The types smallint, integer, and
bigint store whole numbers, that is, numbers without
fractional components, of various ranges. Attempts to store
values outside of the allowed range will result in an error.
The type numeric can store fixed-point numbers with up
to 38 digits without loss of precision. It is especially recommended for
storing monetary amounts and other quantities where exactness is
required. Calculations with numeric values yield exact
results where possible, e.g. addition, subtraction, multiplication.
We use the following terms below: The
precision of a numeric
is the total count of significant digits in the whole number,
that is, the number of digits to both sides of the decimal point.
The scale of a numeric is the
count of decimal digits in the fractional part, to the right of the
decimal point. So the number 23.5141 has a precision of 6 and a
scale of 4. Integers can be considered to have a scale of zero.
The maximum supported precision is 38. Internally, numeric
values are stored as 64-bit values if the precision is smaller or equal
to 18. Precisions over 18 require 128-bit for internal storage.
Processing 128-bit numeric values is often slower than
processing 64-bit values.
Both the maximum precision and the maximum scale of a
numeric column can be
configured. To declare a column of type numeric use
the syntax:
NUMERIC(precision,scale)
The precision must be positive, the scale zero or positive. Alternatively:
NUMERIC(precision)
selects a scale of 0. Specifying:
NUMERIC
selects the maximum precision of 38 and a scale of 0.
The type propagation rules for arithmetic operations with numerics never
decrease the scale and set the precision such that the biggest possible
result will fit into the result type. This may lead to undesired growth of
both scale and precision, especially when chaining multiple arithmetic
operations. Large scale might be undesirable because it takes away from
the digits in front of the decimal point, potentially leading to overflow
errors. Large precision might also be undesirable because numeric values
with precision over 18 internally use 128-bit which may slow down processing.
To avoid this, explicit casts to the desired scale and precision can be added
throughout a query.
Arithmetic operations between a NUMERIC(p1,s1) and a
NUMERIC(p2,s2) have the following results:
Table 1.3. Result Types of Arithmetic Operations with Numeric Operands
| Operator | Result Type |
|---|---|
| + or - |
|
| * |
|
| / |
|
| % |
|
When used in arithmetic operation together with NUMERIC,
DOUBLE PRECISION operands will always give DOUBLE PRECISION results,
SMALLINT behaves the same as NUMERIC(5,0),
INTEGER as NUMERIC(10,0) and BIGINT
as NUMERIC(19,0).
In the SQL standard, as well as in
PostgreSQL and many other database systems,
the types decimal and numeric are equivalent
and both support variable-length precision.
This is unlike Hyper, where
numeric has fixed-length precision and decimal
is not officially supported.
Hyper does not support arbitrary-precision decimal numbers.
If you create an extract of a relational database in Tableau, the extract will always use the
Hyper double precision type, so you only get 15 digits of precision.
However, you can create the extract file using the Hyper API and specify the
numeric type to get up to 38 digits.
Once a numeric value has a precision of over 18, 128-bit
are used for internal storage which can impact the performance of all
subsequent operations.
Storing numeric columns with precision larger than 18 is not available, yet.
The data type double precision is an
inexact, variable-precision numeric type. On all currently supported
platforms, these types are implementations of IEEE
Standard 754 for Binary Floating-Point Arithmetic.
Inexact means that some values cannot be converted exactly to the internal format and are stored as approximations, so that storing and retrieving a value might show slight discrepancies. This is not a limitation of Hyper but an inherent trade-off of using floating-point values. In particular, the following recommendations should be taken into account when using floating-point types:
If you require exact storage and calculations (such as for
monetary amounts), use the numeric type instead.
Aggregations such as sum() on floating-point
values may yield inconsistent results when executed repeatedly
due to parallel computation of aggregates. If you require consistent
results, consider using numeric instead.
Comparing two floating-point values for equality might not always work as expected. Using difference to a small epsilon value is recommended instead.
On all currently supported platforms, the
double precision type has a range of around
1E-307 to 1E+308 with a precision of at least 15 digits. Values that are
too large or too small will cause an error. Rounding might take place if
the precision of an input number is too high. Numbers too close to zero
that are not representable as distinct from zero will cause an underflow
error.
By default, floating point values are output in text form in their shortest precise decimal representation; the decimal value produced is closer to the true stored binary value than to any other value representable in the same binary precision. This value will use at most 17 significant decimal digits.
In addition to ordinary numeric values, the floating-point types have several special values:
Infinity
-Infinity
NaN
These represent the IEEE 754 special values
“infinity”, “negative infinity”, and
“not-a-number”, respectively. When writing these values
as constants in an SQL command, you must put quotes around them,
for example UPDATE table SET x = '-Infinity'. On input,
these strings are recognized in a case-insensitive manner.
IEEE754 specifies that NaN should not compare equal
to any other floating-point value (including NaN itself).
Hyper also supports the SQL-standard
notations float and
float( for specifying
inexact numeric types. Here, p)p specifies
the minimum acceptable precision in binary digits.
However, the p argument is currently ignored
and all float( types are simply
mapped to p)double precision.
float with no precision specified is also mapped to
double precision.