Oracle Built−in Packages- P105 pps

Here are some rules to keep in mind: • The user who executes this procedure must own the new table, and the affected schema must be the same as the user or PUBLIC; alternatively, the use

Notice that each argument to this program is case−sensitive ALTER_TABLE_REFERENCEABLE will not

automatically convert to uppercase the table name you pass to it You must make sure that the table and schema names you provide match exactly the case of the objects found inside the database

You will be able to execute this procedure successfully only if you have the appropriate privileges Here are some rules to keep in mind:

•

The user who executes this procedure must own the new table, and the affected schema must be the same as the user or PUBLIC; alternatively, the user must have ALTER ANY TABLE, SELECT ANY TABLE, and DROP ANY TABLE privileges

•

If the affected schema is PUBLIC (and the user does not have ALTER ANY TABLE, SELECT ANY

TABLE, and DROP ANY TABLE privileges), then the user must own the old mapping table (the table upon which the new table is based) for PUBLIC as well

One tricky aspect to the way this built−in is defined: the default affected_schema is PUBLIC Combine this fact with the previous rules, and you discover that the simplest form of calling the built−in (providing only the table name),

EXECUTE DBMS_DDL.ALTER_TABLE_REFERENCEABLE ('EMPOBJTAB');

will quite often fail with this error:

ORA−20000: insufficient privileges, invalid schema name or

table does not exist

You will say to yourself, "But I own the table!" And then you will realize, "Oh, if I don't specify the affected

schema, then PUBLIC is used and I do not have ALTER ANY TABLE or any of the other privileges needed."

So all I can really do is this,

EXECUTE DBMS_DDL.ALTER_TABLE_REFERENCEABLE ('EMPOBJTAB', USER, USER);

and make sure that the command is applied only to my schema

10.3.4.1.1 Example

Generally, you will use the ALTER_TABLE_REFERENCEABLE procedure when you want to replace an existing object table with a new table of the same structure In this scenario, you will want to make sure that all EOIDS point to this new table

Here are the steps you would take to use ALTER_TABLE_REFERENCEABLE to make this "switch." (These

steps are collected together using an employee table as an example in tabref.sql on the companion disk.)

1

First, you must have an object table already in place Here is the code to create an employee object and then an object table for that object:

CREATE TYPE empobj AS OBJECT (ename VARCHAR2(100), empno INTEGER);

/ CREATE TABLE emp OF empobj /

2

Now I will create a new object table based on the same object as the original table like this:

[Appendix A] What's on the Companion Disk?

CREATE TABLE empNew OF empobj OID AS emp /

3

Next, I transfer the contents of the original emp table to the empNew table In Oracle8, unique object identifiers are automatically assigned to objects when they are stored as "table objects." It turns out that this identifier is stored in a hidden 16−byte RAW field, SYS_NC_OID$ This ID or OID can be referenced from columns in other tables, much like a foreign key I use this in my INSERT to make sure the new table has the same identifier as the old I also must use aliases for my table names for this process to work correctly

INSERT INTO empNew en (SYS_NC_OID$, en) SELECT SYS_NC_OID$, VALUE (eo) FROM emp eo /

4

Now I make the new table referenceable Notice that the name of the table is passed in upper case and

I explicitly pass USER as the schema to avoid the inadvertent usage of PUBLIC

EXECUTE DBMS_DDL.ALTER_TABLE_REFERENCEABLE ('EMPNEW', USER, USER);

5

For my final trick, I swap the names of the tables so that I end up with a new emp table

RENAME emp TO empOld;

RENAME empNew TO emp;

10.3.4.1.2 Exceptions

The ALTER_TABLE_REFERENCEABLE procedure may raise the following exception:

ORA−20000

Insufficient privileges; invalid schema name, or table does not exist

Notice that this exception is not defined in the specification of the package Instead, this program simply calls RAISE_APPLICATION_ERROR with the previous error number This error number may therefore conflict with your own −20NNN error number usages If you embed calls to this procedure inside your application or utility, watch out for the confusion such a conflict can cause

10.3.4.2 The DBMS_DDL.ALTER_TABLE_NOT_REFERENCEABLE procedure (Oracle8 only)

For the affected schema, this procedure simply reverts to the default table referenceable for PUBLIC; that is,

it simply undoes the previous ALTER_TABLE_REFERCEABLE call for this specific schema The header follows:

PROCEDURE DBMS_DDL.ALTER_TABLE_NOT_REFERENCEABLE

(table_name IN VARCHAR2

,table_schema IN VARCHAR2 DEFAULT NULL

,affected_schema IN VARCHAR2 DEFAULT NULL);

Parameters are summarized in the following table

Parameter Description

table_name The name of the table to be made nonreferenceable You cannot use a synonym The

argument is case−sensitive

table_schema

The schema containing the table to be made nonreferenceable If NULL, then the current schema is used The argument is case−sensitive

affected_schema The schema that is to be affected by this change If NULL, then the current schema is

used PUBLIC may not be specified The argument is case−sensitive

This procedure is equivalent to the following SQL statement,

ALTER TABLE [<table_schema>.]<table_name>

NOT REFERENCEABLE FOR <affected_schema>

which is currently neither supported nor available as a DDL statement

10.3.4.2.1 Exceptions

The ALTER_TABLE_NOT_REFERENCEABLE procedure may raise the following exception:

ORA−20000

Insufficient privileges; invalid schema name or table does not exist

Notice that this exception is not defined in the specification of the package Instead, this program simply calls RAISE_APPLICATION_ERROR with the preceding error number This error number may therefore conflict with your own −20NNN error number usages If you embed calls to this procedure inside your application or utility, watch out for the confusion such conflicts can cause

10.2 DBMS_DESCRIBE:

Describing PL/SQL

Program Headers

10.4 DBMS_RANDOM:

Generating Random Numbers (Oracle8 Only)

Copyright (c) 2000 O'Reilly & Associates All rights reserved.

[Appendix A] What's on the Companion Disk?

10.4 DBMS_RANDOM: Generating Random Numbers

(Oracle8 Only)

The DBMS_RANDOM package provides a built−in random number generator utility Oracle Corporation suggests that this package will run faster than generators written in PL/SQL itself because DBMS_RANDOM calls Oracle's internal random number generator

Oracle describes this package as a relatively simple interface for a random number generator, limited to returning an 8−digit number They recommend that you use the DBMS_CRYPTO_TOOLKIT package if you need a more sophisticated engine with more options This package is available with Trusted Oracle.[3]

[3] I must point out that DBMS_RANDOM is built on top of DBMS_CRYPTO_TOOLKIT,

which is not documented in this book

As with any random number generator, before you can obtain any random numbers from DBMS_RANDOM, you must first initialize the package by providing a seed number with DBMS_RANDOM's INITIALIZE procedure You can later reseed the random number generator via RANDOM_SEED When you need a random number, issue a call to the RANDOM, which returns a random number for your use Finally, when you no longer need to use the random number generator, terminate DBMS_RANDOM via the TERMINATE procedure

10.4.1 Getting Started with DBMS_RANDOM

The DBMS_RANDOM package is created when the Oracle database is first installed The dbmsrand.sql script

found in the built−in packages source code directory (described in Chapter 1) contains the source code for this

package's specification This script is called by catoctk.sql, which contains the scripts needed to use the

PL/SQL Cryptographic Toolkit Interface The scripts create the public synonym DBMS_RANDOM for the package and grant EXECUTE privilege on the package to public All Oracle users can reference and make use

of this package

NOTE: If you are running Oracle8 Release 8.0.3, DBMS_RANDOM may not have been

installed in your database In this case, you need to execute the following scripts in the

specified order from within your SYS account: dbmsoctk.sql, prvtoctk.plb, and finally

dbmsrand.sql (it contains both the package specification and body for DBMS_RANDOM).

Table 10.4 summarizes the DBMS_RANDOM programs

Table 10.4: DBMS_RANDOM Programs

INITIALIZE Initializes the random number generator with a seed value No

514

SEED Resets the seed number used to generate the random number No

TERMINATE Terminates the random number generator mechanism No

DBMS_RANDOM does not declare any exceptions or nonprogram elements

10.4.2 DBMS_RANDOM Interface

This section describes the DBMS_RANDOM programs in the order in which they are typically used

10.4.2.1 The DBMS_RANDOM.INITIALIZE procedure

Before you can use the DBMS_RANDOM package, you must initialize it with this program,

PROCEDURE DBMS_RANDOM.INITIALIZE (seed IN BINARY_INTEGER);

where seed is the seed number used in the algorithm to generate a random number You should provide a number with at least five digits to ensure that the value returned by the DBMS_RANDOM.RANDOM

function will be sufficiently, well, random

The INITIALIZE procedure does not assert a purity level with the RESTRICT_REFERENCES pragma

10.4.2.1.1 Example

Here is an example of a call to initialize the DBMS_RANDOM package:

SQL> exec DBMS_RANDOM.INITIALIZE (309666789);

10.4.2.2 The DBMS_RANDOM.SEED procedure (Oracle8 only)

Once the random number generator has been initialized, you can change the seed value used by

DBMS_RANDOM with the SEED procedure The specification is,

PROCEDURE DBMS_RANDOM.SEED(seed IN BINARY_INTEGER);

where seed is the seed number used in the algorithm to generate a random number As with INITIALIZE, you should provide a number with at least five digits to ensure that the value returned by the

DBMS_RANDOM.RANDOM function will be sufficiently random

The SEED procedure does not assert a purity level with the RESTRICT_REFERENCES pragma

10.4.2.2.1 Example

Here is an example of a call to reseed the DBMS_RANDOM package:

SQL> exec DBMS_RANDOM.SEED (455663349);

10.4.2.3 The DBMS_RANDOM.RANDOM function (Oracle8 only)

Call the RANDOM function to retrieve a random number

FUNCTION DBMS_RANDOM.RANDOM RETURN BINARY_INTEGER;

The RANDOM runction does not assert a purity level with the RESTRICT_REFERENCES pragma

[Appendix A] What's on the Companion Disk?