Re: How Can I use OO concepts? - Mailing list pgsql-novice

On Wed, 2005-11-23 at 16:47 +0000, flavio@gral.org.br wrote:
> Hi ALL
>
> I´m trying to test OO concepts using postgres. I took an Oracle example, extracted from
> http://savtechno.com/ViewOfORDBMS.html
> As I know Oracle has more OO mature concepts, and Postgres? Where is OO into PostgreSQL
> (weak point in table?)
>
> How can I do the same as Oracle using Postgres? Please correct me.
...
>
> My PostgreSQL Solution ???? OO??? I think not.
>
> CREATE TABLE Employee (
>   Name      VARCHAR(20),
>   Salary    NUMERIC(6,2)
> );
> CREATE TABLE Programmer (
>   Language   VARCHAR(12),
>   Project    VARCHAR(30)
> )INHERITS  (Employee);
> CREATE TABLE Representative  (
>   Region    VARCHAR(30)
> ) INHERITS (Employee);

The mixed-case table names are a bad idea.  They are automatically
folded to lower-case unless double-quoted; it just causes confusion.

You have already created tables, so the next three lines are not needed:
> CREATE TABLE employees AS SELECT * FROM Employee;
> CREATE TABLE programmers AS SELECT * FROM  Programmer;
> CREATE TABLE representatives AS SELECT * FROM  Representative;
(you could create views, but why bother?)

> INSERT INTO employees  VALUES ('Sylvia Karsen', 3000.00);
> INSERT INTO programmers VALUES ('William Helprin', 400.00, 'C++', 'Seestorm');
> INSERT INTO representatives VALUES ('Akiko Yokomoto', 500.00, 'Asia');

Insert directly into the tables you created first.

> ORACLE Query Output
> SELECT e.Name FROM employees e;
> Would be:
>
> Name
> --------------------
> Sylvia Karsen

In PostgreSQL, that returns all records in the hierarchy.

This is how it goes in PostgreSQL:

junk=# CREATE TABLE Employee (
junk(#   Name      VARCHAR(20),
junk(#   Salary    NUMERIC(6,2)
junk(# );
CREATE TABLE
junk=# CREATE TABLE Programmer (
junk(#   Language   VARCHAR(12),
junk(#   Project    VARCHAR(30)
junk(# )INHERITS  (Employee);
CREATE TABLE
junk=# CREATE TABLE Representative  (
junk(#   Region    VARCHAR(30)
junk(# ) INHERITS (Employee);
CREATE TABLE
junk=# INSERT INTO employee  VALUES ('Sylvia Karsen', 3000.00);
INSERT 0 1
junk=# INSERT INTO programmer VALUES ('William Helprin', 400.00, 'C++',
'Seestorm');
INSERT 0 1
junk=# INSERT INTO representative VALUES ('Akiko Yokomoto', 500.00,
'Asia');
INSERT 0 1
junk=# SELECT e.Name FROM employee e;
      name
-----------------
 Sylvia Karsen
 William Helprin
 Akiko Yokomoto
(3 rows)

junk=# SELECT e.Name FROM ONLY employee e;
     name
---------------
 Sylvia Karsen
(1 row)

junk=#


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Oliver Elphick                                          olly@lfix.co.uk
Isle of Wight                              http://www.lfix.co.uk/oliver
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