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Home -> Community -> Usenet -> comp.databases.theory -> Re: Does Codd's view of a relational database differ from that of Date&Darwin? [M.Gittens]

Re: Does Codd's view of a relational database differ from that of Date&Darwin? [M.Gittens]

From: Jon Heggland <heggland_at_idi.ntnu.no>
Date: Mon, 13 Jun 2005 10:17:46 +0200
Message-ID: <MPG.1d175f959ed68625989693@news.ntnu.no>


In article <oFcqe.12059$F7.3016_at_news-server.bigpond.net.au>, hobbit_at_southern_seaweed.com.op says...
> > What does NULL + NULL evaluate to? NULL or 0?
>
>
> It's dependent upon the resident SET command and the
> data type of the operands. Here is the MS SQL ref,

This is just for strings. Does it have similar functionality for other data types?

> (the null value is treated as an empty string).

Sheesh. I thought this was a bug in Oracle only. What if you want to actually store an empty string? Or is it just in this particular case that NULLs and empty strings are considered the same?

> > How about the sum of an attribute of an empty relation? Or of a column
> > with just NULLs?
>
> Dependent upon the SET command.

Even when no NULLs are involved, as in the empty relation?

-- 
Jon
Received on Mon Jun 13 2005 - 03:17:46 CDT

Original text of this message

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