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

Here is sql to show the 3 valued logic in Oracle (I don't have nor do I want access to ProCobol to test)

create table three_val_logic (test_3_val char(5));

insert into three_val_logic values ('TRUE');
insert into three_val_logic values ('FALSE')
insert into three_val_logic values (NULL)

commit;

select * from three_val_logic;

TEST_
-----
TRUE
FALSE


select rownum, test_3_val
from three_val_logic
where test_3_val = 'TRUE';

    ROWNUM TEST_
---------- -----
         1 TRUE

select rownum, test_3_val
from three_val_logic
where test_3_val = 'FALSE';

    ROWNUM TEST_
---------- -----
         1 FALSE

select rownum, test_3_val
from three_val_logic
where test_3_val != 'TRUE';

    ROWNUM TEST_
---------- -----
         1 FALSE

select rownum, test_3_val
from three_val_logic
where test_3_val != 'FALSE';

    ROWNUM TEST_
---------- -----
         1 TRUE

select rownum, test_3_val
from three_val_logic
where test_3_val IS NOT NULL;

    ROWNUM TEST_
---------- -----
         1 TRUE
         2 FALSE

pl/sql version
 1  declare
  2     cursor three_val_cur is select rownum, test_3_val from three_val_logic;
  3     three_val_rec three_val_cur%rowtype;
  4  begin
  5     for three_val_rec in three_val_cur
  6     loop
  7        if three_val_rec.test_3_val = 'TRUE'
  8        then
  9           dbms_output.put_line('Line '||three_val_rec.rownum||' is TRUE');
 10        elsif three_val_rec.test_3_val = 'FALSE'
 11        then
 12           dbms_output.put_line('Line '||three_val_rec.rownum||' is FALSE');
 13        else
 14           dbms_output.put_line('Line '||three_val_rec.rownum||' is not TRUE 
and not FALSE');
 15        end if;
 16        if three_val_rec.test_3_val != 'TRUE'
 17        then
 18           dbms_output.put_line('Line '||three_val_rec.rownum||' is NOT 
TRUE');
 19        elsif three_val_rec.test_3_val != 'FALSE'
 20        then
 21           dbms_output.put_line('Line '||three_val_rec.rownum||' is NOT 
FALSE');
 22        else
 23           dbms_output.put_line('Line '||three_val_rec.rownum||' is not NOT 
TRUE and not NOT FALSE');
 24        end if;
 25     end loop;
 26* end;
SQL> /
Line 1 is TRUE
Line 1 is NOT FALSE
Line 2 is FALSE
Line 2 is NOT TRUE
Line 3 is not TRUE and not FALSE
Line 3 is not NOT TRUE and not NOT FALSE

So a NULL in pl/sql fails the equality comparison test. Its the not NOT TRUE and not NOT FALSE which seem to mess people up. In 2 valued logic NOT TRUE = FALSE and NOT FALSE = TRUE, but this is not the case in 3 valued logic.

Enjoy the Ardberg... I'm jonesing for The Glenmorangie Burgundy Wood Finish or 18 year old Highland Park.

Daniel



Jared.Still@xxxxxxxxxxx wrote: 


 > 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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