MacLochlainns Weblog

A couple students stumbled on the MySQL on-line documentation today. Specifically, they didn’t find instructions on how a non-root user could change their password. I’ve also added this as an explanation on the MySQL documentation for 12.5.1.6. SET PASSWORD Syntax page.

You reset your own password when you’re not the root user with this syntax:

mysql> SET PASSWORD = PASSWORD('new_password');

This is simple syntax but carries a risk if you walk away from your terminal because somebody can run it without needing to know the original user password. Oracle requires that you know the original password if you use this syntax:

SQL> PASSWORD
Changing password FOR PLSQL
OLD password:
NEW password:
Retype NEW password:
Password changed

If you think that you’re safe walking away from an Oracle SQL*Plus console, check this because it doesn’t require knowing the current password either.

SQL> SHOW USER
USER IS "PLSQL"
SQL> ALTER USER plsql IDENTIFIED BY plsql;
USER altered.

Don’t walk away, always lock your terminal or use the QUIT command to exit MySQL. This generally prevents somebody hijacking your password. You can check this post if you’re interested in changing the root password when you don’t have it to begin with. Hope this helps a few folks.

The longest outstanding question I’ve received is on how you can aggregate the number of rows in a nested table (one inside another). If you need a refresher on joining non-collection columns to nested columns, you should check this earlier blog post.

The basic premise is boils down to two points. One are you trying to get a count of the elements in the nested collection, or a count of the elements in the nested collection based on one or more columns in the nested table. There are two ways to perform a basic count of the nested line numbers, and one way to perform the other. You find out how to perform both in the post.

1. You can run the following script to create a sample data environment. It is re-runnable, and designed to run on either Oracle Database 10g or 11g.

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-- Conditionally delete objects in reverse dependency order.
BEGIN
  FOR i IN (SELECT   object_name
            ,        object_type
            FROM     user_objects
            WHERE    object_type IN ('TABLE','SEQUENCE','TYPE')
            AND      object_name IN ('TELEPHONE_TYPE','TELEPHONE_TABLE'
                                    ,'CONTACT_BOOK','CONTACT_BOOK_S1')
            ORDER BY object_type, object_name DESC) LOOP
    EXECUTE IMMEDIATE 'DROP '||i.object_type||' '||i.object_name;
  END LOOP;
END;
/
 
-- Create a composite data type (structure) and collection.
CREATE TYPE telephone_type AS OBJECT
( country_code   VARCHAR2(3)
, prefix_code    VARCHAR2(5)
, phone_number   VARCHAR2(9));
/
 
CREATE TYPE telephone_table AS TABLE OF telephone_type;
/
 
-- Create a table with a nested composite table and sequence.
CREATE TABLE contact_book
( contact_book_id   NUMBER
, first_name        VARCHAR2(30)
, last_name         VARCHAR2(30)
, telephone_numbers TELEPHONE_TABLE )
NESTED TABLE telephone_numbers STORE AS telephone_struct;
 
CREATE SEQUENCE contact_book_s1;
 
-- Insert two rows of data.
INSERT INTO contact_book
VALUES
( contact_book_s1.nextval
,'Harry','Potter'
,telephone_table(telephone_type('44','20','7299 2127')
                ,telephone_type('44','17','8926 8115')
                ,telephone_type('44','18','3344 5566')
                ,telephone_type('44','72','9878 5436')));
 
INSERT INTO contact_book
VALUES
( contact_book_s1.nextval
,'Weasley','Ronald'
,telephone_table(telephone_type('40','021','407 47 46')
                ,telephone_type('44','19','4088 1062')
                ,telephone_type('44','21','4075 5066')));

2. You can query the line numbers of the nested table by the scalar columns two ways. The first uses the CARDINALITY function introduced in Oracle 10g. The second leverages a CROSS JOIN and traditional aggregation tools.

2(a). Using the CARDINALITY function is generally the simplest and best approach to this problem:

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SELECT first_name
,      last_name
,      CARDINALITY(telephone_numbers) list
FROM   contact_book;

This yield the following data set:

FIRST_NAME   LAST_NAME      LIST
------------ ------------ ------
Harry        Potter            4
Weasley      Ronald            3

2(b). Using the traditional CROSS JOIN and GROUP BY clause:

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SELECT   cj.first_name
,        cj.last_name
,        COUNT(*)
FROM    (SELECT *
         FROM contact_book cb CROSS JOIN TABLE(cb.telephone_numbers)) cj
GROUP BY cj.first_name
,        cj.last_name;

This yield the following data set:

FIRST_NAME   LAST_NAME      LIST
------------ ------------ ------
Harry        Potter            4
Ronald       Weasley           3

3. If you wanted to know how many numbers where in the nested table by country code, you need to solve the problem through a CROSS JOIN and GROUP BY clause, like this:

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SELECT   cj.first_name
,        cj.last_name
,        cj.country_code
,        COUNT(*)
FROM    (SELECT *
         FROM contact_book cb CROSS JOIN TABLE(cb.telephone_numbers)) cj
GROUP BY cj.first_name
,        cj.last_name
,        cj.country_code;

This yield the following data set:

FIRST_NAME   LAST_NAME    COUNTRY_CODE   LIST
------------ ------------ ------------ ------
Harry        Potter       44                4
Ronald       Weasley      44                2
Ronald       Weasley      40                1

If I captured the basics of the question, great. If there are more questions, please let me know.

Somebody asked me to post some examples of Large Object syntax. I checked Chapter 9 of the Oracle Database SecureFiles and Large Object Developer’s Guide, and I agree an example or two would be helpful. I’ve provided CREATE and ALTER statements.

Here’s a sample CREATE TABLE statement for a CLOB, BLOB, and BFILE:

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CREATE TABLE item
( item_id             NUMBER        CONSTRAINT pk_item    PRIMARY KEY
, item_barcode        VARCHAR2(20)  CONSTRAINT nn_item_1  NOT NULL
, item_type           NUMBER        CONSTRAINT nn_item_2  NOT NULL
, item_title          VARCHAR2(60)  CONSTRAINT nn_item_3  NOT NULL
, item_subtitle       VARCHAR2(60) 
, item_desc           CLOB          CONSTRAINT nn_item_4  NOT NULL
, item_blob           BLOB
, item_photo          BFILE
, item_rating         VARCHAR2(8)   CONSTRAINT nn_item_5  NOT NULL
, item_rating_agency  VARCHAR2(4)   CONSTRAINT nn_item_6  NOT NULL
, item_release_date   DATE          CONSTRAINT nn_item_7  NOT NULL
, created_by          NUMBER        CONSTRAINT nn_item_8  NOT NULL
, creation_date       DATE          CONSTRAINT nn_item_9  NOT NULL
, last_updated_by     NUMBER        CONSTRAINT nn_item_10 NOT NULL
, last_update_date    DATE          CONSTRAINT nn_item_11 NOT NULL
, CONSTRAINT fk_item_1                      FOREIGN KEY(item_type)
  REFERENCES common_lookup(common_lookup_id)
, CONSTRAINT fk_item_2                      FOREIGN KEY(created_by)
  REFERENCES system_user(system_user_id)
, CONSTRAINT fk_item_3                      FOREIGN KEY(last_updated_by)
  REFERENCES system_user(system_user_id))
  LOB (item_desc) STORE AS BASICFILE item_desc
  (TABLESPACE users ENABLE STORAGE IN ROW CHUNK 32768
   PCTVERSION 10 NOCACHE LOGGING
   STORAGE (INITIAL 1048576
            NEXT 1048576
            MINEXTENTS 1
            MAXEXTENTS 2147483645))  
, LOB (item_blob) STORE AS item_blob
  (TABLESPACE users ENABLE STORAGE IN ROW CHUNK 32768
   PCTVERSION 10 NOCACHE LOGGING
   STORAGE (INITIAL 1048576
            NEXT 1048576
            MINEXTENTS 1
            MAXEXTENTS 2147483645));

If you attempt to make the CHUNK size greater than 32,768, it will raise an ORA-22851: invalid CHUNK LOB storage option value error.

Here’s a sample ALTER TABLE statement that adds a new large object column to a table. You can’t modify an existing large object column. You raise an ORA-22859: invalid modification of columns error when you try it. If you need to make modifications, check this post form last year on re-organizing LOB indexes.

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ALTER TABLE item ADD (another CLOB)
LOB (another) STORE AS BASICFILE item_clob
(TABLESPACE users ENABLE STORAGE IN ROW CHUNK 32768
 PCTVERSION 10 NOCACHE LOGGING
 STORAGE (INITIAL 1048576
          NEXT 1048576
          MINEXTENTS 1
          MAXEXTENTS 2147483645));

This all makes sense, but hold on there’s a potential problem when you add a large object column to a table. I’m not sure it’s a bug but I’ll probably open a TAR on it later in the week (arghhhh! I once worked in Oracle Support. :-)). Anyway, here’s what I found:

If you drop and recreate the table, you can encounter an ORA-01430 error. It appears that the large object is really hanging out in the catalog. As soon as you try to re-add it, you get the error.

If you describe the table after recreating it, you’ll see the following:

SQL> DESCRIBE item
 Name                                      Null?    Type
 ----------------------------------------- -------- ---------------
 ITEM_ID                                   NOT NULL NUMBER
 ITEM_BARCODE                              NOT NULL VARCHAR2(20)
 ITEM_TYPE                                 NOT NULL NUMBER
 ITEM_TITLE                                NOT NULL VARCHAR2(60)
 ITEM_SUBTITLE                                      VARCHAR2(60)
 ITEM_DESC                                 NOT NULL CLOB
 ITEM_BLOB                                          BLOB
 ITEM_PHOTO                                         BINARY FILE LOB
 ITEM_RATING                               NOT NULL VARCHAR2(8)
 ITEM_RATING_AGENCY                        NOT NULL VARCHAR2(4)
 ITEM_RELEASE_DATE                         NOT NULL DATE
 CREATED_BY                                NOT NULL NUMBER
 CREATION_DATE                             NOT NULL DATE
 LAST_UPDATED_BY                           NOT NULL NUMBER
 LAST_UPDATE_DATE                          NOT NULL DATE

Also, if you run the following query with the DBMS_METADATA package, the column doesn’t exist in the table defintion:

SELECT dbms_metadata.get_ddl('TABLE','ITEM') FROM dual;

If try to run the ALTER statement to add the column that doesn’t appear to exist, you’ll get the following message in Oracle 11.1.0.7.0:

ALTER TABLE item ADD (another CLOB)
                      *
ERROR at line 1:
ORA-01430: COLUMN being added already EXISTS IN TABLE

If you rerun the DBMS_METADATA.GET_DDL query, it’ll be there in the table definition. Also, in its non-existence but existent state (ghost-state), there’s nothing in the DBA_LOB, or DBA_SEGMENT views. You can find a query to check large object segments and indexes here. My questions is where has it gone, why is it there, and did I do something wrong because this looks like basic functionality.

If you know the mystery or the existence of a bug, please post a comment.

It’s the end of our Spring term, and yes occasionally somebody can’t sign on to their Oracle instance because their event log is full. They get the following message on Winodws:

C:\>sqlplus / AS sysdba
 
SQL*Plus: Release 11.1.0.7.0 - Production ON Wed Jul 15 10:19:37 2009
 
Copyright (c) 1982, 2008, Oracle.  ALL rights reserved.
 
Enter password:
ERROR:
ORA-28056: Writing audit records TO Windows Event Log failed

The fix is simple, just delete your items from your Windows’ event log. 😉

I was playing around with some external table filtering examples, and I stumbled on a restriction that I’d previously missed. You can’t filter external data with SQL functions, like REGEXP_LIKE. Unfortunately, the limitation applies to equality and non-equality validation in combination with the AND and OR operators.

CREATE TABLE item_load
( item_title    VARCHAR2(60)
, item_subtitle VARCHAR2(60)
, release_date  DATE)
  ORGANIZATION EXTERNAL
  ( TYPE oracle_loader
    DEFAULT DIRECTORY upload_source
    ACCESS PARAMETERS
    ( RECORDS DELIMITED BY NEWLINE CHARACTERSET US7ASCII
      BADFILE     'UPLOAD_LOG':'item_load.bad'
      DISCARDFILE 'UPLOAD_LOG':'item_load.dis'
      LOGFILE     'UPLOAD_LOG':'item_load.log'
      LOAD WHEN (REGEXP_LIKE(item_title,'^Harry.'))
      FIELDS TERMINATED BY ','
      OPTIONALLY ENCLOSED BY "'"
      MISSING FIELD VALUES ARE NULL )
      LOCATION ('item_load.csv'))
REJECT LIMIT UNLIMITED;

It threw the following exception, which includes a new error message (at least for me), the KUP-01005. I suppose that basically means you can’t use function calls inside external table access parameters but I couldn’t find it in the documentation. Chapter 13 (the lucky number) in the Oracle Database Utilities 11g manual only provides examples of equality and non-equality.

Here’s the raise exception for those using external tables:

SQL> SELECT * FROM item_load;
SELECT * FROM item_load
              *
ERROR at line 1:
ORA-29913: error IN executing ODCIEXTTABLEOPEN callout
ORA-29400: DATA cartridge error
KUP-00554: error encountered while parsing access parameters
KUP-01005: syntax error: found "(": expecting one OF: "equal, notequal"
KUP-01007: at line 5 COLUMN 29

I couldn’t leave it alone, I tried the LIKE operator and a jackpot – another new error message:

KUP-01008: the bad identifier was: LIKE

It makes sense, it’s the 13th of July and two days before the new Harry Potter flick, therefore it must be Chapter 13 was calling to me. Hope this helps a few folks.

The fact that you could raise an ugly error when you query an external table always bothered me. I looked at Java stored procedures as the best solution initially. That was overkill. This afternoon, while writing about them for the new PL/SQL Workboook, it became clear. The fix is really easy.

If you know little to nothing about external tables, you can go read this earlier post. Likewise, if you don’t know about objects and object collection, you can refer to this post. Having provided you with the context, here’s an example that eliminates errors when querying an external table without an external file.

1. Create an external file, like this character table.

CREATE TABLE CHARACTER
( character_id NUMBER
, first_name VARCHAR2(20)
, last_name VARCHAR2(20))
  ORGANIZATION EXTERNAL
  ( TYPE oracle_loader
    DEFAULT DIRECTORY download
    ACCESS PARAMETERS
    ( RECORDS DELIMITED BY NEWLINE CHARACTERSET US7ASCII
      BADFILE     'DOWNLOAD':'character.bad'
      DISCARDFILE 'DOWNLOAD':'character.dis'
      LOGFILE     'DOWNLOAD':'character.log'
      FIELDS TERMINATED BY ','
      OPTIONALLY ENCLOSED BY "'"
      MISSING FIELD VALUES ARE NULL )
    LOCATION ('character.csv'))
REJECT LIMIT UNLIMITED;

2. Create a user-defined object type that mirrors your external table defintion, like this:

CREATE OR REPLACE TYPE character_obj IS OBJECT
( character_id NUMBER
, first_name VARCHAR2(20)
, last_name VARCHAR2(20));
/

3. Create a user-defined collection of your object type, like

CREATE OR REPLACE TYPE character_obj_table IS TABLE OF character_obj;
/

4. Create a function that returns the user-defined collection of your object type, like

CREATE OR REPLACE FUNCTION character_source
RETURN character_obj_table IS
  c          NUMBER;
  collection CHARACTER_OBJ_TABLE := character_obj_table();
BEGIN
  FOR i IN (SELECT * FROM CHARACTER) LOOP
    collection.EXTEND;
    collection(c) := character_obj( i.character_id
                                  , i.first_name
                                  , i.last_name);
    c := c + 1;
  END LOOP;
  RETURN collection;
EXCEPTION
  WHEN OTHERS THEN
    RETURN collection;
END;
/

5. Query the function not the table, which returns no rows found when the file doesn’t physically exist, or the file contains no data. Lastly, the function returns the data when it is there.

SELECT * FROM TABLE(character_source);

Hope this helps those using external tables to avoid the typical error stack:

SELECT * FROM CHARACTER
*
ERROR at line 1:
ORA-29913: error IN executing ODCIEXTTABLEOPEN callout
ORA-29400: DATA cartridge error
KUP-04040: file CHARACTER.csv IN CHARACTER NOT found

I also wrote this older post about confirming it in the database catalog. If you any follow-up suggestions, please let me know.

While SQL Developer is a nice tool and free, Toad is still an awesome development platform, albeit for Windows. In fact, it was annoying to have to install the Microsoft .NET Framework before installing it. It is free for MySQL!

Since my students have to do all their work in Oracle and then port it to MySQL, I demonstrate Quest’s Toad for MySQL’s at the end of the term. I don’t want them to leverage the automatic ERD diagramming while they’re learning how to do it.

There’s only one real trick to making automatic ERD diagramming work. That trick requires that you write your loading scripts for the Inno DB and use referential integrity constraints. My sample Video Store scripts for my database class are updated for MySQL referential integrity.

Unlike the friendly CASCADE CONSTRAINTS clause you can use in Oracle, MySQL won’t let you create a re-runnable script with only DDL statements. Actually, the constraint comes from the InnoDB engine. You must issue a specialized InnoDB command before running your script:

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-- This enables dropping tables with foreign key dependencies.
-- It is specific to the InnoDB Engine.
SET FOREIGN_KEY_CHECKS = 0;

Primary keys are a bit different from Oracle and it appears you can’t name them, at least I couldn’t see how to do it. Here’s an example of primary and foreign key constraints in MySQL. The primary key is inline and the foreign key constraints are out of line. This example from the downloadable scripts uses self referencing foreign key constraints.

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CREATE TABLE system_user
( system_user_id              INT UNSIGNED PRIMARY KEY AUTO_INCREMENT
, system_user_name            CHAR(20)     NOT NULL
, system_user_group_id        INT UNSIGNED NOT NULL
, system_user_type            INT UNSIGNED NOT NULL
, first_name                  CHAR(20)
, middle_name                 CHAR(20)
, last_name                   CHAR(20)
, created_by                  INT UNSIGNED NOT NULL
, creation_date               DATE         NOT NULL
, last_updated_by             INT UNSIGNED NOT NULL
, last_update_date            DATE         NOT NULL
, KEY system_user_fk1 (created_by)
, CONSTRAINT system_user_fk1 FOREIGN KEY (created_by)
  REFERENCES system_user (system_user_id)
, KEY system_user_fk2 (last_updated_by)
, CONSTRAINT system_user_fk2 FOREIGN KEY (last_updated_by)
  REFERENCES system_user (system_user_id)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

Once installed (instructions are here) and connected to the MySQL database, you simply click the ERD icon in the top panel and drag the tables onto the canvas. You’ll see something like this (by the way click on the image to see its full size):

Have fun with it. It’ll be interesting to see how Oracle positions MySQL when they own it. My hunch is that they’ll continue to sell it and provide it as an open source product.

I finally got around to summarizing how to use PHP to store, retrieve, and display CLOBs and BLOBs from an Oracle database. I think too often we default to BFILEs. I put all the code in zip files with instructions and suggestions for locations. This is really the second entry that goes with configuring Zend Server Community Edition or the DEPRECATED Zend Core for Oracle.

If you’re new to PHP, check out the Underground PHP and Oracle book from Christopher Jones and Alison Holloway. It’s FREE!

The Oracle LOB Processing entry is in this blog page. I know it means another click, but I’ll probably add and modify it over time. If you’ve got time and interest, take a look and let me know what you think and what improvements you’d like to see. Thanks.

My students have to do their group labs in Oracle and then port them individually to MySQL. Most of the conversion resolves around dates because Oracle spoils us with their simplicity in their SQL dialect.

For example, if we wanted to add 9 days to today’s system date (June 27, 2009) we can do this in Oracle:

SQL> SELECT SYSDATE + 9 FROM dual;

It prints

06-JUL-09

If we tried the equivalent in MySQL, we get a null because it treats any day value over 31 as a null. The maximum date in any month is 31, regardless of month. If you add more days than the maximum number minus your current date, you return a null. This is because adding a day never changes the month, and that yields invalid dates. In MySQL, you need to make this calculation with the adddate() or date_add() functions because they’ll increment months and years.

By way of example, if we only added four to today’s date (June 27, 2009) and formatted the output as a date, it works

mysql> SELECT str_to_date(utc_date() + 4,'%Y%m%d');

We’d get this:

+--------------------------------------+
| str_to_date(utc_date() + 4,'%Y%m%d') |
+--------------------------------------+
| 2009-06-31                           |
+--------------------------------------+

I always wanted an extra day in June. 😉

In short, there are three possible non-dates in February that format as dates, and one day in every thirty day month. I’ve a hunch this is a bug (I’ve logged a bug and they’ve verified it and moved it to triage).

The correct way to perform this calculation in MySQL is to use either the adddate() or date_add() functions. They take the same arguments. Here’s a quick example:

mysql> SELECT adddate(utc_date(),INTERVAL 9 DAY);

It yields the correct date:

+------------------------------------+
| adddate(utc_date(),INTERVAL 9 DAY) |
+------------------------------------+
| 2009-07-06                         |
+------------------------------------+

I know this answers a student email but I hope it helps a few others too.

Never change something that works! Not really, but sometimes you feel that way. Especially, when you toast 5 to 10 minutes working through an undocumented behavior in PL/SQL. You’d think after writing it for 19 years, I’d have seen it all but not so.

I was working through a tried and true example from Chapter 14 of the Oracle Database 11g PL/SQL Programming book to prepare for teaching my class tomorrow, when I found this nice quirk. It took a few minutes to figure out what was happening, but here it is so you don’t have to look for it too. You can only use variable names that are attributes of the object type as formal parameters in object type constructors. If you try to vary it, you’ll trigger the following exception:

LINE/COL ERROR
-------- -----------------------------------------------------------------
4/11     PL/SQL: Item ignored
4/26     PLS-00307: too many declarations OF 'HELLO_THERE' MATCH this CALL
6/5      PL/SQL: Statement ignored
6/13     PLS-00320: the declaration OF the TYPE OF this expression IS incomplete OR malformed

All I did to trigger this exception was change the who variable to make it scope specific, like iv_who for instance variable, pv_who for parameter variable, and lv_who for local variable.

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CREATE OR REPLACE TYPE hello_there IS OBJECT
( iv_who VARCHAR2(20)
, CONSTRUCTOR FUNCTION hello_there
  RETURN SELF AS RESULT
, CONSTRUCTOR FUNCTION hello_there
  ( pv_who VARCHAR2 )
  RETURN SELF AS RESULT
, MEMBER FUNCTION get_who RETURN VARCHAR2
, MEMBER PROCEDURE set_who (pv_who VARCHAR2)
, MEMBER PROCEDURE to_string )
INSTANTIABLE NOT FINAL;
/

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CREATE OR REPLACE TYPE BODY hello_there IS
 
  CONSTRUCTOR FUNCTION hello_there RETURN SELF AS RESULT IS
    hello HELLO_THERE := hello_there('Generic Object.');
  BEGIN
    SELF := hello;
    RETURN;
  END hello_there;
 
  CONSTRUCTOR FUNCTION hello_there (pv_who VARCHAR2) RETURN SELF AS RESULT IS
 
  BEGIN
    SELF.iv_who := pv_who;
    RETURN;
  END hello_there;
 
  MEMBER FUNCTION get_who RETURN VARCHAR2 IS
  BEGIN
    RETURN SELF.iv_who;
  END get_who;
 
  MEMBER PROCEDURE set_who (pv_who VARCHAR2) IS
  BEGIN
    SELF.iv_who := pv_who;
  END set_who;
 
  MEMBER PROCEDURE to_string IS
  BEGIN
    dbms_output.put_line('Hello '||SELF.iv_who);
  END to_string;
 
END;
/

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CREATE OR REPLACE TYPE hello_there IS OBJECT
( iv_who VARCHAR2(20)
, CONSTRUCTOR FUNCTION hello_there
  RETURN SELF AS RESULT
, CONSTRUCTOR FUNCTION hello_there
  ( iv_who VARCHAR2 )
  RETURN SELF AS RESULT
, MEMBER FUNCTION get_who RETURN VARCHAR2
, MEMBER PROCEDURE set_who (pv_who VARCHAR2)
, MEMBER PROCEDURE to_string )
INSTANTIABLE NOT FINAL;
/

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CREATE OR REPLACE TYPE BODY hello_there IS
 
  CONSTRUCTOR FUNCTION hello_there RETURN SELF AS RESULT IS
    hello HELLO_THERE := hello_there('Generic Object.');
  BEGIN
    SELF := hello;
    RETURN;
  END hello_there;
 
  CONSTRUCTOR FUNCTION hello_there (iv_who VARCHAR2) RETURN SELF AS RESULT IS
 
  BEGIN
    SELF.iv_who := iv_who;
    RETURN;
  END hello_there;
 
  MEMBER FUNCTION get_who RETURN VARCHAR2 IS
  BEGIN
    RETURN SELF.iv_who;
  END get_who;
 
  MEMBER PROCEDURE set_who (pv_who VARCHAR2) IS
  BEGIN
    SELF.iv_who := pv_who;
  END set_who;
 
  MEMBER PROCEDURE to_string IS
  BEGIN
    dbms_output.put_line('Hello '||SELF.iv_who);
  END to_string;
 
END;
/

This is certainly interesting. I’ve no clue why such a limitation exists. The name of a parameter list member in the constructor should be independent from the attribute of a user object.