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Re: trouble selecting from array

From: "Merlin Moncure" <mmoncure(at)gmail(dot)com>
To: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: brian <brian(at)zijn-digital(dot)com>, pgsql-general(at)postgresql(dot)org
Subject: Re: trouble selecting from array
Date: 2008-03-28 18:19:55
Message-ID: (view raw or whole thread)
Lists: pgsql-general
On Thu, Mar 27, 2008 at 8:58 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>  If you want a sub-array you need to use the slice notation, eg
>  tdr_tags[2:2][1:2]

The slice approach is not a general fact there seems to
be no way to convert an array of N dimensions to N-1 dimensions except
in the special case of N=1.  One side effect of this is that the
_pg_expand_array approaches which I was about to suggest to the OP
only work for one dimensional arrays.

reading the archives, you wrote:
"Because it isn't a slice expression --- you used colon nowhere, so the
result type is going to be text not text[].  (Remember that the parser
must determine the expression's result type at parse time, so whether
there are enough subscripts can't enter into this.)  Our alternatives
here are to throw a subscripting error or return NULL.  I'd personally
have gone with throwing an error, I think, but it seems far too late to
revisit that decision."

is there not enough information available to the parser to reduce the
expression dimensions by one?


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