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Re: Operator class group proposal

From: Gregory Stark <gsstark(at)mit(dot)edu>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Operator class group proposal
Date: 2006-12-22 21:21:25
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Lists: pgsql-hackers
Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:

> No, what you'll get is something like
> 	int4var::float8 float8eq float8var
> which is perfectly mergejoinable ... however, it's not clear that the
> planner will make very good estimates about the value of the cast
> expression.  I'm not sure if it's worth introducing a pile more
> crosstype operators to change that situation --- improving
> the selectivity functions to handle casts better might be a wiser
> approach.

So the only reason we needed the cross-data-type operators was to get better
estimates? I thought without them you couldn't get an index-based plan at all.

  Gregory Stark

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