Overview of Predefined PL/SQL Datatypes
A scalar type has no internal components. It holds a single value, such as a number or
character string.
A composite type has internal components that can be manipulated individually, such
as the elements of an array.
A reference type holds values, called pointers, that designate other program items.
A LOB type holds values, called lob locators, that specify the location of large objects,
such as text blocks or graphic images, that are stored separately from other database
data.
Figure 3–1 shows the predefined PL/SQL datatypes. The scalar types fall into four
families, which store number, character, Boolean, and date/time data, respectively.
BINARY_INTEGER(PLS_INTEGER)
You use the BINARY_INTEGER datatype to store signed integers. Its magnitude range
is -2**31 .. 2**31.
BINARY_INTEGER values require less storage than NUMBER values. Arithmetic
operations on BINARY_INTEGER values are also faster than NUMBER arithmetic.
BINARY_INTEGER and PLS_INTEGER both have these advantages. Because PLS_
INTEGER was faster in earlier releases, you might use it instead of BINARY_INTEGER
in code that will run on older databases.
PLS_INTEGER
You use the PLS_INTEGER datatype to store signed integers. Its magnitude range is
-2**31 .. 2**31. PLS_INTEGER values require less storage than NUMBER values. Also,
PLS_INTEGER operations use machine arithmetic, so they are faster than NUMBER and
BINARY_INTEGER operations, which use library arithmetic. For efficiency, use PLS_
INTEGER for all calculations that fall within its magnitude range.
Although PLS_INTEGER and BINARY_INTEGER have the same magnitude range,
they are not fully compatible. When a PLS_INTEGER calculation overflows, an
exception is raised. However, when a BINARY_INTEGER calculation overflows, no
exception is raised if the result is assigned to a NUMBER variable.
Because of this small semantic difference, you might want to continue using BINARY_
INTEGER in old applications for compatibility. In new applications, always use PLS_
INTEGER for better performance.
结论:在版本低的库中使用BINARY_INTEGER，在版本高的库中，推荐使用PLS_INTEGER
NUMBER(我们最常用的NUMBER)
You use the NUMBER datatype to store fixed-point or floating-point numbers. Its
magnitude range is 1E-130 .. 10E125. If the value of an expression falls outside this
range, you get a numeric overflow or underflow error. You can specify precision, which is
the total number of digits, and scale, which is the number of digits to the right of the
decimal point. The syntax follows:
NUMBER[(precision,scale)]
To declare fixed-point numbers, for which you must specify scale, use the following
form:
NUMBER(precision,scale)
To declare floating-point numbers, for which you cannot specify precision or scale
because the decimal point can "float" to any position, use the following form:
NUMBER
To declare integers, which have no decimal point, use this form:
NUMBER(precision) -- same as NUMBER(precision,0)
You cannot use constants or variables to specify precision and scale; you must use
integer literals. The maximum precision of a NUMBER value is 38 decimal digits. If you
do not specify precision, it defaults to 38 or the maximum supported by your system,
whichever is less.
Scale, which can range from -84 to 127, determines where rounding occurs. For
instance, a scale of 2 rounds to the nearest hundredth (3.456 becomes 3.46). A negative
scale rounds to the left of the decimal point. For example, a scale of -3 rounds to the
nearest thousand (3456 becomes 3000). A scale of 0 rounds to the nearest whole
number. If you do not specify scale, it defaults to 0.