From: Warren Young
Date: January 24 2007 4:41pm
Subject: Re: troubles with 2.2.0
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Королев Илья wrote:
> 
> Query q;
> q << "...";
> cerr << q.preview() << endl;
> q.execute();

preview() has always been heavy-handed.  This could be a case where it 
only worked accidentally before, not because it was really supposed to work.

The problem with preview() is that it must "freeze" the query into a 
final form, as opposed to the intermediate form it uses when holding the 
query prior to execution.  preview() almost goes completely through the 
actual query finalization process in order to freeze the query, so it 
can have unfortunate side effects.  Probably the change is due to the 
Query call chain reorganization, needed to allow nulls in queries.

I'm not saying that's what's going on for certain, but that's my best 
guess right now.  Unfortunately, I'm not likely to be able to spend much 
more time on it for a while.