Re: [GENERAL][SQL] Getting multiple field unique index to distinguish NULLs.

Is this problem with NULLS being treated as distinct values only apparent
in regards to Indices? If you do a Select Distinct or a Group By using
these fields does it display the duplicate rows with nulls? I know this
doesn't offer any help but I was just curious...

Beth :-)
_______________________________________________
/ Beth L Strohmayer / Software Engineer _____)
/ ITT Industries, Systems Division (_____|______________________
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At 11:37 AM 09/10/1999 , Stuart Rison wrote:
>Hi Tom,
>
>On Fri, 10 Sep 1999, Tom Lane wrote:
>
> > > The problem is that the indexing considers all NULLs to be distinct thus:
> >
> > Don't use NULLs ... declare the columns as NOT NULL, and select some
> > special value for the fields you want to consider unused. Zero maybe,
> > or an empty string if the columns are text.
> >
>
>Fair enough, and indeed it's a solution I've been using but, for the sake
>of argument, what if I couldn't do it?
>
>I though of using a index and functions such as:
>
>CREATE UNIQUE INDEX myscheme_idx ON myscheme_funcat
>(level1, null_to_zero(level2), null_to_zero(level3),
>null_to_zero(level4));
>
>but saddly, you can't use functions in that way to define indices or at
>least not in this way...
>
>I tried
>
>CREATE UNIQUE INDEX myscheme_idx ON myscheme_funcat
>(make_key(level1,level2,level3,level4) text_ops);
>
>Where make_key essentially concatenates the levels into a '.' separated
>key (e.g. 1 or 1.2.1 or 2.4.1.6).
>
>Now this would work except that there's a problem with pl/pgSQL such that
>when you pass several values to a plpgsql function and one of them is
>NULL, then all values passed to the function become NULL.
>
>The solution would be something like:
>
>CREATE UNIQUE INDEX myscheme_idx ON myscheme_funcat
>(make_key(level1,null_to_zero(level2),null_to_zero(level3),
>null_to_zero(level4));
>
>But saddly you can't have "sub-function" in the CREATE INDEX statement.
>
>So:
>
>1) yes, the solution would be to use 0 or somesuch token value for 'NULL'
>2) but I wondered if anybody had ventured into the kind of stuff mentioned
>above
>3) and if anybody have solved the pl/pgSQL 'issue' that turns all values
>to NULL?
>
>Regards,
>
>Stuart.
>
>
>************