Can this be done (see use of segment_4 at end of query)?

This returns the correct value when a valid url_title is hard-coded, but not with the segment variable.

I have tried curly braces/no curly braces, single quotes/no single quotes, double quotes/no double quotes.

ExpressionEngine 1.6.3 - 20080319

would be the way to go.

The rule for exp:query is to use single quotes.

But I’ll bet the problem is you need to use {segment_3} instead of {segment_4}.

Yes, in fact that’s the case, but {segment_4} works correctly in a nearby {exp:weblog”:entries} tag. Why?

Without seeing the template you’re using this with, it’s hard to say.