From: Emi Lu <emilu@encs.concordia.ca>
To: John Fabiani <johnf@jfcomputer.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: Dates and NULL's`
Date: Tue, 10 May 2011 16:36:45 -0400
Message-ID: <4DC9A1DD.5070700@encs.concordia.ca> (raw)
In-Reply-To: <201105101024.23612.johnf@jfcomputer.com>
References: <201105100948.41392.johnf@jfcomputer.com>
<BANLkTina8jK3f_p0xynxgzQhpL2aCUsL6A@mail.gmail.com>
<201105101024.23612.johnf@jfcomputer.com>
>>> Where mydate>= "2011/04/01"::date and mydate<= "2011/04/30"::date
>>> With the above where will the NULL's be selected????
>>
>> Here is what I get when I try:
>>
>> spi=> SELECT NULL::DATE>= '2011-04-01'::DATE AND NULL::DATE<=
>> '2011-04-30'::DATE;
>> ?column?
>> ----------
>>
>> (1 row)
>>
>>
>> spi=> SELECT (NULL::DATE>= '2011-04-01'::DATE AND NULL::DATE<=
>> '2011-04-30'::DATE) IS TRUE;
>> ?column?
>> ----------
>> f
>> (1 row)
>>
>>
>> spi=> SELECT (NULL::DATE>= '2011-04-01'::DATE AND NULL::DATE<=
>> '2011-04-30'::DATE) IS FALSE;
>> ?column?
>> ----------
>> f
>> (1 row)
>>
>>
>> spi=> SELECT (NULL::DATE>= '2011-04-01'::DATE AND NULL::DATE<=
>> '2011-04-30'::DATE) IS UNKNOWN;
>> ?column?
>> ----------
>> t
>> (1 row)
> Sorry Richard, I do not understand.
>
> It looks like you are saying the NULLS will be returned too
As a summary:
============================================
(1)
null:date COMPARE 'real date'::DATE
Will always return NUll, so you will not get the record returned at all!
(2) examples he provided:
. (null:date COMPARE 'real date'::DATE) IS NULL;
. (null:date COMPARE 'real date'::DATE) IS UNKNOWN;
Null returns true.
(3) null is true/false;
returns false
Emi
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To: pgsql-sql@postgresql.org
Cc: emilu@encs.concordia.ca, johnf@jfcomputer.com
Subject: Re: Dates and NULL's`
In-Reply-To: <4DC9A1DD.5070700@encs.concordia.ca>
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