Skip site navigation (1) Skip section navigation (2)

Re: [HACKERS] A small type extension example for the contrib directory (fwd)

From: Zeugswetter Andreas DBT <Andreas(dot)Zeugswetter(at)telecom(dot)at>
To: "'pgsql-hackers(at)hub(dot)org'" <pgsql-hackers(at)hub(dot)org>
Subject: Re: [HACKERS] A small type extension example for the contrib directory (fwd)
Date: 1998-01-26 13:15:58
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
I wrote:
>>> In the second query, the first two rows have been grouped, but
>>> they not be since b is NULL?  I thought that NULL != NULL?
>Note that:
>NULL <> NULL		is false
>NULL = NULL			is false

This was wrong, I digged up some more docu and found:
<something> op NULL		is unknown    note that there exists a
third boolean state (name it ?)
`Unknown values occur when part of an expression that uses an arithmetic
operator is null.`
If a whole where expression evaluates to unknown the row is not chosen.
not:	t -> f, f -> t, ? -> ?
and:	? and t -> ?, ? and f -> f, ? and ? -> ?
or:	t or ? -> t, f or ? -> ?, ? or ? -> ?

Order by: `Null values are ordered as less than values that are not
	NULL {>|<|<=|>=}  value		is unknown


pgsql-hackers by date

Next:From: Bruce MomjianDate: 1998-01-26 15:08:07
Subject: Re: [HACKERS] Re: [QUESTIONS] How is PostgreSQL doing?
Previous:From: Zeugswetter Andreas DBTDate: 1998-01-26 11:51:54
Subject: Re: [HACKERS] Group By, NULL values and inconsistent behaviour.

Privacy Policy | About PostgreSQL
Copyright © 1996-2017 The PostgreSQL Global Development Group