Re: [HACKERS] writing a MIN(RECORD) aggregate

[Decibel!]

On Mar 20, 2008, at 2:23 PM, Sam Mason wrote:

I'm trying to write a version of the MIN aggregate for values of RECORD type. I'm somewhat stuck on getting type information about the argument out, I can determine how many attributes it's got but I can't seem to do any better than that. Does anyone have any good pointers into the code

for places to help me understand what's happening?


doing things like:

  SELECT i, (MIN((j,k))).k
  FROM tbl
  GROUP BY i;

The reason for doing this is mainly because I think it'd be nicer to be

How is that any better than SELECT i, min(k) FROM tbl GROUP BY i ?

instead of:

  SELECT DISTINCT ON (i) i, k
  FROM tbl
  ORDER BY i,j,k;


ON method.

Which as far as I can tell should produce identical results, except the first has cleaner semantics. It also allows you to combine MIN and MAX in the same query, giving the value of k for the smallest and largest j in this example--requiring two queries if it was done using the DISTINCT

I don't see how min(record) even allows for that.


--
Decibel!, aka Jim C. Nasby, Database Architect  [EMAIL PROTECTED]
Give your computer some brain candy! www.distributed.net Team #1828

I'm not saying that min/avg/max/etc(RECORD) wouldn't be useful; I'm just failing to see the use in these examples.

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