RE: Useful Oracle books - C.J. Date theory vs. practicality

From: Lex de Haan <lex.de.haan_at_naturaljoin.nl>
Date: Fri, 28 May 2004 21:43:04 +0200
Message-ID: <JFEEIGBIDOCCDALDIPLNEEOOCDAA.lex.de.haan@naturaljoin.nl>

Hi Jared,

the difference becomes apparent if you try a condition like the following:

'Mort Subite' = NULL

This condition is neither TRUE nor FALSE; it evaluates to UNKNOWN.

According to three-valued logic, NOT UNKNOWN evaluates to UNKNOWN; therefore, both statements will execute their ELSE branch; so the first one executes statement 2, and the second one executes statement 1.

My math teacher (many moons ago) usually would say at this point: QED.

Kind regards,
Lex.

visit my website at http://www.naturaljoin.nl

-----Original Message-----
From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org]On Behalf Of Jared.Still_at_radisys.com
Sent: Friday, May 28, 2004 20:24
To: oracle-l_at_freelists.org
Subject: RE: Useful Oracle books - C.J. Date theory vs. practicality

> just for fun, check out these two commands:
>
> IF (some condition) THEN (statement 1) ELSE (statement 2);
> IF NOT (some condition) THEN (statement 2) ELSE (statement 1);
>
> regardless the contents of your data structures,
> in COBOL these two are equivalent but in PL/SQL they are not!

You've really lost me here.

12:22:41 rsysdevdb.radisys.com - jkstill_at_dv01 SQL> 12:22:46 rsysdevdb.radisys.com - jkstill_at_dv01 SQL> l 1 begin
2

  3     if true then
  4             dbms_output.put_line('TRUE');
  5     else
  6             dbms_output.put_line('FALSE');
  7     end if;
  8
  9     if not true then
 10             dbms_output.put_line('FALSE');
 11     else
 12             dbms_output.put_line('TRUE');
 13     end if;

14
15* end;
12:22:47 rsysdevdb.radisys.com - jkstill_at_dv01 SQL> / TRUE
TRUE PL/SQL procedure successfully completed.

Maybe I need a slug of Ardberg to understand.

Jared

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Received on Fri May 28 2004 - 14:41:36 CDT