Re: cardinality()

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Andrew Dunstan <andrew(at)dunslane(dot)net>, Grzegorz Jaskiewicz <gj(at)pointblue(dot)com(dot)pl>, PostgreSQL-development Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: cardinality()
Date: 2009-03-01 17:40:16
Message-ID: 13073.1235929216@sss.pgh.pa.us
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I wrote:
> The standard doesn't have multi-dimensional arrays, so it's entirely
> possible that somewhere in it there is wording that makes cardinality()
> equivalent to the length of the first dimension. But I concur with
> Andrew that this is flat wrong when extended to m-d arrays.

I poked around in the SQL:2008 draft a bit. AFAICT the most precise
statement about cardinality() is in 6.27 <numeric value function>:

<cardinality expression> ::=
CARDINALITY<left paren> <collection value expression> <right paren>

7) The result of <cardinality expression> is the number of elements of
the result of the <collection value expression>.

Now the standard is only considering 1-D arrays, but I fail to see any
way that it could be argued that the appropriate reading of "number of
elements" for a multi-D array is the length of the first dimension.
So I think Andrew is right and we need to fix our implementation of
cardinality() while we still can.

regards, tom lane

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