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

From: Powell, Mark D <mark.powell_at_eds.com>
Date: Fri, 28 May 2004 15:48:24 -0400
Message-ID: <564DE4477544D411AD2C00508BDF0B6A1CE0AB65@usahm018.exmi01.exch.eds.com>

I think the point was if part of some condition was Null then the statement is not true, but is not false either as technically the result is unknown so in pl/sql you potentially should have a construct that looks like

If true

...
Else if false
...
Else [it is null so]

I have seen more than one bug traced to the failure of a developer to remember that in pl/sql just because something is not true that does not mean it is false. Failure to remember this results in attempts to find rows for the FALSE condition when there is no value to be used to query for those rows.

In native COBOL there is only True and False. However if you use COBOL with an RDBMS both Oracle and DB2 provide a null value indicator feature that can be used to allow program logic to properly handle the data. No matter what language is used when the data comes from an RDBMS that supports NULLs this issue of TRUE/ FALSE/ NULL probably exists.

Just adding to the noise level.
-- Mark D Powell --

-----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 3:24 PM
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 - 14:46:11 CDT