Oracle® Database PL/SQL Packages and Types Reference 10g Release 2 (10.2) Part Number B14258-01 |
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The DBMS_RANDOM
package provides a built-in random number generator. DBMS_RANDOM
is not intended for cryptography.
This chapter contains the following topics:
Security Model
Operational Notes
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.
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, userid, 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.
Table 75-1 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 |
This 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), while the overloaded function gets a random Oracle number x, where x is greater than or equal to low and less than high |
Note:
The INITIALIZE Procedure, RANDOM Procedure and the TERMINATE Procedure are all obsolete and, while currently supported, are included in this release for legacy reasons only.This procedure initializes the generator (but see Usage Notes).
Syntax
DBMS_RANDOM.INITIALIZE ( val IN BINARY_INTEGER);
Pragmas
PRAGMA restrict_references (initialize, WNDS)
Parameters
Table 75-2 INITIALIZE Procedure Parameters
Parameter | Description |
---|---|
val |
The seed number used to generate a random number. |
Usage Notes
This procedure is obsolete as it simply calls the SEED Procedures.
This function returns random numbers in a standard normal distribution.
Syntax
DBMS_RANDOM.NORMAL RETURN NUMBER;
Pragmas
PRAGMA restrict_references (normal, WNDS)
Return Values
This procedure generates a random number (but see Usage Notes).
Syntax
DBMS_RANDOM.RANDOM RETURN binary_integer;
Pragmas
PRAGMA restrict_references (random, WNDS)
Return Values
Table 75-4 RANDOM Procedure Parameters
Parameter | Description |
---|---|
binary_integer |
Returns a random integer greater or equal to -power(2,31) and less than power(2,31). |
Usage Notes
This procedure is obsolete and, although it is currently supported, it should not be used.
This procedure resets the seed.
Syntax
DBMS_RANDOM.SEED ( seed IN BINARY_INTEGER); DBMS_RANDOM.SEED ( seed IN VARCHAR2);
Pragmas
PRAGMA restrict_references (seed, WNDS);
Parameters
Table 75-5 SEED Procedure Parameters
Parameter | Description |
---|---|
seed |
Seed number or string used to generate a random number. |
Usage Notes
The seed can be a string up to length 2000.
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 75-6 STRING Function Parameters
Parameter | Description |
---|---|
opt |
Specifies what the returning string looks like:
Otherwise the returning string is in uppercase alpha characters. |
len |
The length of the returning string. |
Return Values
When you are finished with the package, call the TERMINATE procedure (but see Usage Notes)
Syntax
DBMS_RANDOM.TERMINATE
Usage Notes
This procedure performs no function and, although it is currently supported, it is obsolete and should not be used.
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 75-8 VALUE Function Parameters
Parameter | Description |
---|---|
low |
The lowest number in a range from which to generate a random number. The number generated may be equal to low. |
high |
The highest number below which to generate a random number. The number generated will be less than high. |
Return Values