108 DBMS_RANDOM

The DBMS_RANDOM package provides a built-in random number generator. DBMS_RANDOM is not intended for cryptography.

This chapter contains the following topics:

Using DBMS_RANDOM

Deprecated Subprograms

Note:

Oracle recommends that you do not use deprecated procedures in new applications. Support for deprecated features is for backward compatibility only.

The following subprograms are deprecated with Oracle Database 11g:

Security Model

This package should be installed as SYS. By default, the package is initialized with the current user name, current time down to the second, and the current session. Oracle recommends that users who need to execute this package should be given EXECUTE privilege explicitly and should not rely on PUBLIC EXECUTE privilege.

Operational Notes

  • DBMS_RANDOM.RANDOM produces integers in [-2^^31, 2^^31).

  • DBMS_RANDOM.VALUE produces numbers in [0,1) with 38 digits of precision.

DBMS_RANDOM can be explicitly initialized, but does not need to be initialized before calling the random number generator. It will automatically initialize with the date, user ID, and process ID if no explicit initialization is performed.

If this package is seeded twice with the same seed, then accessed in the same way, it will produce the same results in both cases.

In some cases, such as when testing, you may want the sequence of random numbers to be the same on every run. In that case, you seed the generator with a constant value by calling one of the overloads of DBMS_RANDOM.SEED. To produce different output for every run, simply to omit the call to "Seed" and the system will choose a suitable seed for you.

Summary of DBMS_RANDOM Subprograms

Table 108-1 DBMS_RANDOM Package Subprograms

Subprogram Description

INITIALIZE Procedure

Initializes the package with a seed value

NORMAL Function

Returns random numbers in a normal distribution

RANDOM Procedure

Generates a random number

SEED Procedures

Resets the seed

STRING Function

Gets a random string

TERMINATE Procedure

Terminates package

VALUE Functions

Gets a random number, greater than or equal to 0 and less than 1, with 38 digits to the right of the decimal (38-digit precision), while the overloaded function gets a random Oracle number x, where x is greater than or equal to low and less than high

INITIALIZE Procedure

This procedure initializes the generator.

Note:

This procedure is deprecated with Release 11gR1 and, although currently supported, it should not be used.

Syntax

DBMS_RANDOM.INITIALIZE (
   val  IN  BINARY_INTEGER);

Pragmas

PRAGMA restrict_references (initialize, WNDS);

Parameters

Table 108-2 INITIALIZE Procedure Parameters

Parameter Description

val

Seed number used to generate a random number

Usage Notes

This procedure is obsolete as it simply calls the SEED Procedures.

NORMAL Function

This function returns random numbers in a standard normal distribution.

Syntax

DBMS_RANDOM.NORMAL
  RETURN NUMBER;

Pragmas

PRAGMA restrict_references (normal, WNDS);

Return Values

Table 108-3 NORMAL Function Parameters

Parameter Description

number

Returns a random number

RANDOM Procedure

This procedure generates a random number.

Note:

This procedure is deprecated with Release 11gR1 and, although currently supported, it should not be used.

Syntax

DBMS_RANDOM.RANDOM
   RETURN binary_integer;

Pragmas

PRAGMA restrict_references (random, WNDS);

Return Values

Table 108-4 RANDOM Procedure Parameters

Parameter Description

binary_integer

Returns a random integer greater or equal to -power(2,31) and less than power(2,31)

SEED Procedures

This procedure resets the seed.

Syntax

DBMS_RANDOM.SEED (
   val  IN  BINARY_INTEGER);

DBMS_RANDOM.SEED (
   val  IN  VARCHAR2);

Pragmas

PRAGMA restrict_references (seed, WNDS);

Parameters

Table 108-5 SEED Procedure Parameters

Parameter Description

val

Seed number or string used to generate a random number

Usage Notes

The seed can be a string up to length 2000.

STRING Function

This function gets a random string.

Syntax

DBMS_RANDOM.STRING
   opt  IN  CHAR,
   len  IN  NUMBER)
  RETURN VARCHAR2;

Pragmas

PRAGMA restrict_references (string, WNDS);

Parameters

Table 108-6 STRING Function Parameters

Parameter Description

opt

Specifies what the returning string looks like:

  • 'u', 'U' - returning string in uppercase alpha characters

  • 'l', 'L' - returning string in lowercase alpha characters

  • 'a', 'A' - returning string in mixed case alpha characters

  • 'x', 'X' - returning string in uppercase alpha-numeric characters

  • 'p', 'P' - returning string in any printable characters.

Otherwise the returning string is in uppercase alpha characters.

len

Length of the returning string

Return Values

Table 108-7 STRING Function Return Values

Parameter Description

VARCHAR2

Returns a VARCHAR2

TERMINATE Procedure

When you are finished with the package, call the TERMINATE procedure.

Note:

This procedure is deprecated with Release 11gR1 and, although currently supported, it should not be used.

Syntax

DBMS_RANDOM.TERMINATE;

VALUE Functions

The basic function gets a random number, greater than or equal to 0 and less than 1, with 38 digits to the right of the decimal (38-digit precision). Alternatively, you can get a random Oracle number x, where x is greater than or equal to low and less than high.

Syntax

DBMS_RANDOM.VALUE
  RETURN NUMBER;

DBMS_RANDOM.VALUE(
  low  IN  NUMBER,
  high IN  NUMBER)
RETURN NUMBER;

Parameters

Table 108-8 VALUE Function Parameters

Parameter Description

low

Lowest number in a range from which to generate a random number. The number generated may be equal to low

high

Highest number below which to generate a random number. The number generated will be less than high

Return Values

Table 108-9 VALUE Function Return Values

Parameter Description

NUMBER

Returns an Oracle Number