Обсуждение: binding a variable to NULL in perl-DBD

Greetings,

I'm trying to determine how to pass "NULL" to a variable, specifically in 
the conditional section of a SQL statement:

SELECT moo
FROM foo aa
WHERE field1 = ?
AND field2 = ?

Sometimes at the command line, when running the perl-DBD script, I would 
like the select statement to reflect:

SELECT moo
FROM foo aa
WHERE field1 = 'goo'
AND field2 IS NULL

Much thanks in advance,

Max Pyziur
pyz@brama.com

    Max Pyziur wrote:

> I'm trying to determine how to pass "NULL" to a variable, specifically in 
> the conditional section of a SQL statement:
> 
> SELECT moo
> FROM foo aa
> WHERE field1 = ?
> AND field2 = ?

Perl's undef is used to pass NULL as a literal but field=NULL
will never be true.

> SELECT moo
> FROM foo aa
> WHERE field1 = 'goo'
> AND field2 IS NULL

You may use:
WHERE field1 = ?
AND field2 IS NOT DISTINCT FROM ?

which conveys the idea that field2 must be equal to the value passed,
and works as expected with both non-NULL literals and NULL (undef).

Best regards,
-- 
Daniel
PostgreSQL-powered mail user agent and storage: http://www.manitou-mail.org

On Thu, 22 Aug 2013, Daniel Verite wrote:

>     Max Pyziur wrote:
>
>> I'm trying to determine how to pass "NULL" to a variable, specifically in
>> the conditional section of a SQL statement:
>>
>> SELECT moo
>> FROM foo aa
>> WHERE field1 = ?
>> AND field2 = ?
>
> Perl's undef is used to pass NULL as a literal but field=NULL
> will never be true.
>
>> SELECT moo
>> FROM foo aa
>> WHERE field1 = 'goo'
>> AND field2 IS NULL
>
> You may use:
> WHERE field1 = ?
> AND field2 IS NOT DISTINCT FROM ?

Much thanks for your help. The way that I'm making this work is that on 
the command line for the argument of interest I use the word NULL, then in 
the perl code I have:
if ($FIELD2_CODE eq "NULL") { undef($FIELD2_CODE); }

and then in the SQL:
"AND field2 IS NOT DISTINCT FROM ?" seems to work

Do I have a correct understanding of Postgres SQL's vernacular and 
application here?

> which conveys the idea that field2 must be equal to the value passed,
> and works as expected with both non-NULL literals and NULL (undef).
>
> Best regards,
>

Thank you again,

Max Pyziur
pyz@brama.com