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pls_integer类型
今天在看一个触发器代码的时候碰到了一个pls_integer类型,以前没碰到过,记录一下:
PLS_INTEGER可以存储一个有符号的整形值，其精度范围和BINARY_INTEGER一样，是：-2^31~2^31。
PLS_INTEGER和NUMBER比较起来，其优点是：
1).占有较少的存储空间；
2).可以直接进行算术运算（在NUMBER上不能直接进行算术运算，如果要计算，NUMBER必须先被转换成二进制）。所以在进行算术的时候PLS_INTEGER比NUMBER和BINARY_INTEGER快一些。
PLS_INTEGER和BINARY_INTEGER区别：
PLS_INTEGER进行的运算发生溢出的时候，会触发异常。但是当BINARY_INTEGER运算发生溢出时，如果可以指派给一个NUMBER变量(没有超出NUMBER的精度范围)的话就不会触发异常。
Benefits of Using
PLS_INTEGER Datatype in PL/SQL
If you have a whole-number counter, for example in a loop or record counter, consider using a datatype ofPLS_INTEGER instead of INTEGER or NUMBER. When declaring an integer variable,PLS_INTEGER
is the most efficient numeric datatype because its values require less
storage than INTEGER or NUMBER values, which are represented internally
as 22-byte Oracle numbers. Also,PLS_INTEGER operations
use machine arithmetic, so they are faster than BINARY_INTEGER, INTEGER, or NUMBER operations, which use library arithmetic.
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PLS_INTEGER Datatype
You use the PLS_INTEGER datatype to store signed integers. Its magnitude range is -2147483648 to 2147483647, represented in 32 bits. PLS_INTEGER values require less storage than NUMBER values and NUMBER subtypes. Also, PLS_INTEGER operations use hardware arithmetic, so they are faster than NUMBER operations, which use library arithmetic. For efficiency, use PLS_INTEGER for all calculations that fall within its magnitude range. For calculations outside the range of PLS_INTEGER, you can use the INTEGER datatype.
Note:
The BINARY_INTEGER and PLS_INTEGER datatypes are identical. See "Change to the BINARY_INTEGER Datatype".
When a calculation with two PLS_INTEGER datatypes overflows the magnitude range of PLS_INTEGER, an overflow exception is raised even if the result is assigned to a NUMBER datatype.
You use the PLS_INTEGER datatype to store signed integers. Its magnitude range is -2147483648 to 2147483647, represented in 32 bits. PLS_INTEGER values require less storage than NUMBER values and NUMBER subtypes. Also, PLS_INTEGER operations use hardware arithmetic, so they are faster than NUMBER operations, which use library arithmetic. For efficiency, use PLS_INTEGER for all calculations that fall within its magnitude range. For calculations outside the range of PLS_INTEGER, you can use the INTEGER datatype.
Note:
The BINARY_INTEGER and PLS_INTEGER datatypes are identical. See "Change to the BINARY_INTEGER Datatype".
When a calculation with two PLS_INTEGER datatypes overflows the magnitude range of PLS_INTEGER, an overflow exception is raised even if the result is assigned to a NUMBER datatype.
tips:1）pls_integer类型也是数字类型，但和number类型不同，number可以存储实数，而pls_integer只能存储-2147483647到+2147483647之间的整数，如果使用pls_integer类型时发生溢出，系统将会报错。
2）binary_integer与pls_integer类似，在9.2版本以前大量使用，从9.2以后，从Oracle内部一些组件可以看的出，大有被pls_integer取代之势(pls_integer比binary_integer具有更少的存储开销和更好的访问性能，所以Oracle从9.2以后推荐你尽量能使用pls_integer就使用pls_integer)。它也是只能存储-2147483647到+2147483647之间的整数。
3）在oracle 11g中，又增加了一个新的类似的数据类型simple_integer,不过simple_integer不能包含空值，它的取值范围是[-2147483648..2147483647]。在11g中，simple_integer相对pls_integer在性能上又有所提高，如果在实际的pl/sql中既不需要overflow检查也不会包含null值，Oracle建议你使用simple_integer.
来源：http://www.itpub.net/thread-1106923-1-1.html
注：Binary_Integer
与 Pls_Integer 都是整型类型.
Binary_Integer类型变量值计算是由Oracle来执行，不会出现溢出，但是执行速度较慢，因为它是由Oracle模拟执行。而Pls_Integer的执行是由硬件即直接由CPU来运算，因而会出现溢出，但其执行速度较前者快许多。