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

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.

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-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx]On
Behalf Of Jared.Still@xxxxxxxxxxx
Sent: Friday, May 28, 2004 20:24
To: oracle-l@xxxxxxxxxxxxx
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@dv01 SQL>
12:22:46 rsysdevdb.radisys.com - jkstill@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@dv01 SQL> /
TRUE
TRUE

PL/SQL procedure successfully completed.

Maybe I need a slug of Ardberg to understand.

Jared

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