Обсуждение: BOOLEAN data type?

Folks:
I had assumed that the BOOL column type was a tru boolean.  That is, I
wrote some functions on the understand that, given table def:

CREATE TABLE order_details (order_detail_id SERIAL NOT NULL PRIMARY KEY,detail_id INT4 NOT NULL,order_usq INT4 NOT
NULL,detail_requiredBOOL DEFAULT FALSE );
 

That the following query:

SELECT detail_id FROM order_detials
WHERE order_usq = 7703 AND detail_required;
... should be equivalent to:

SELECT detail_id FROM order_detials
WHERE order_usq = 7703 AND detail_required = TRUE;

However, in testing (7.1 RC2), the query turned out to mean this:

SELECT detail_id FROM order_detials
WHERE order_usq = 7703 AND detail_required IS NOT NULL;

... throwing off a lot of my results until I figured it out.

Can someone explain this to me?  I thought the whole point of a BOOL
data type was that it could be treated as a Boolean value, and used for
testing and comparison without and "= TRUE" or "= FALSE".  What's going
on here?

-Josh



______AGLIO DATABASE SOLUTIONS___________________________                                      Josh Berkus Complete
informationtechnology      josh@agliodbs.com  and data management solutions       (415) 565-7293 for law firms, small
businesses       fax 621-2533   and non-profit organizations.      San Francisco
 

Josh Berkus writes:

> That the following query:
>
> SELECT detail_id FROM order_detials
> WHERE order_usq = 7703 AND detail_required;
>
>  ... should be equivalent to:
>
> SELECT detail_id FROM order_detials
> WHERE order_usq = 7703 AND detail_required = TRUE;
>
> However, in testing (7.1 RC2), the query turned out to mean this:
>
> SELECT detail_id FROM order_detials
> WHERE order_usq = 7703 AND detail_required IS NOT NULL;

No way.  You're doing something wrong.  How about showing the data that
makes you believe this?

-- 
Peter Eisentraut      peter_e@gmx.net       http://yi.org/peter-e/

"Josh Berkus" <josh@agliodbs.com> writes:
> Can someone explain this to me?

Are you taking into account that SQL booleans are actually three-valued?
They can be TRUE, FALSE, or NULL (NULL taken as meaning "don't know").
        regards, tom lane

Peter,
> No way.  You're doing something wrong.  How about showing the data
> that
> makes you believe this?

Hey, take it easy.  It was only a technical question / potential issue.
Not a personal criticism.

Based on your implied assertion that the queries *should* be working in
a Boolean fashion, I took them apart and re-built them ... and it turned
out to be a data problem in a linked table (a unique index was dropped
somehow without my awareness while altering the tables).

So Booleans are working properly, and you can relax now.

-Josh Berkus








______AGLIO DATABASE SOLUTIONS___________________________                                      Josh Berkus Complete
informationtechnology      josh@agliodbs.com  and data management solutions       (415) 565-7293 for law firms, small
businesses       fax 621-2533   and non-profit organizations.      San Francisco
 

Tom,

> Are you taking into account that SQL booleans are actually
> three-valued?
> They can be TRUE, FALSE, or NULL (NULL taken as meaning "don't
> know").

That turned out not to be the issue, but that's good information to
have.  I'll need to remember to make all of my BOOLEAN columns NOT NULL
DEFAULT FALSE.

-Josh


______AGLIO DATABASE SOLUTIONS___________________________                                      Josh Berkus Complete
informationtechnology      josh@agliodbs.com  and data management solutions       (415) 565-7293 for law firms, small
businesses       fax 621-2533   and non-profit organizations.      San Francisco