Message-Id: <3.0.5.32.20000717121856.022cd100@mail.rhyme.com.au>
Date: Mon, 17 Jul 2000 12:18:56 +1000
To: Carolyn Lu Wong <carolyn@kss.net.au>,
	"pgsql-sql@postgresql.org" <pgsql-sql@postgresql.org>
From: Philip Warner <pjw@rhyme.com.au>
Subject: Re: SQL question
In-Reply-To: <39726A5C.B6B45856@kss.net.au>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"

At 12:07 17/07/00 +1000, Carolyn Lu Wong wrote:
>I have table with the following definition:
>
>	create table table1(
>		account_no	int4,
>		start_date_tme	datetime
>		....
>	);
>
>The table may contain null values for start_date_time.
>
>When I run the following SQL query, it fails:
>
>	select * from table1
>	where start_date_time::date >= '01/01/2000'::date 
>	and start_date_time::date <= '01/01/2001'::date;
>
>I get error message 'Unable to convert null datetime to date.
>
>It's fine if I run the same SQL query with added condition as follows:
>
>	select * from table1
>>	where account_no = 1
>	and start_date_time::date >= '01/01/2000'::date 
>	and start_date_time::date <= '01/01/2001'::date;
>
>Is this a bug? Or there's an logical explaination for this?

The most logical explanation is that there are no null values in
start_date_time when account_no = 1.

Try 
    select count(*) from table1 where account_no = 1 and start_date_time is
null;

and see if you get 0.


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