Re: Boolean casting in 7.3 -> changed?

On Thursday 28 November 2002 00:18, Tom Lane wrote:
> Peter Eisentraut <peter_e(at)gmx(dot)net> writes:
> > Ian Barwick writes:
> >> "Casting integers to boolean (for example, 0::bool) is no longer
> >> allowed, use '0'::bool instead".
> >
> > This advice would probably only cause more confusion, because we are now
> > moving into the direction that character strings are no longer acceptable
> > as numeric data.
>
> Yes, phrased that way it's just misleading.

OK, what I am trying to say is something like:

"If you are upgrading an application to PostgreSQL 7.3
and are having problems with boolean casts which look like
0::bool or 1::bool, which previously worked without any problem,
(although not explicitly supported) you will need to rewrite them
to use the values listed here:

http://www.postgresql.org/idocs/index.php?datatype-boolean.html .

Doing things like '0'::bool will also work but is not recommended."

because that's a problem I came across but found no mention of,
so I thought I would point it out for the benefit of anyone else
who might encounter it ;-)

For reference, the reason why I was casting integer-like literals
to boolean in the first place is:
- Perl application used to run on a combination of MySQL and Oracle;
- Perl doesn't have a boolean data type, but the values 0 and 1
in scalar context do the job just as well;
- MySQL happily accepts literals for boolean column types,
e.g. INSERT INTO table_with_boolean_column
(boolean_column)
VALUES (0)
- the same statement in PostgreSQL produced
"ERROR: Attribute 'boolean_column' is of type 'bool' but expression is of type 'int4'
You will need to rewrite or cast the expression"
- so I did what it said and wrote 0::bool - and thought
no further of it, until now when I began the upgrade.
- being in a bit of a hurry I put tried '0'::bool and it worked...
- having rtfm, obviously just '0' and no mucking about with casting
is better anyway...

Peter Eisentraut <peter_e(at)gmx(dot)net> wrote:
> Note that
>
> x <> 0
>
> is also a perfectly good way to convert integers to booleans, and a more
> portable one at that.

Ah, that is a useful tip.

Thanks for the information

Ian Barwick
barwick(at)gmx(dot)net