RE: Why oh why is this join not working?

> Now, I can refer to t1.class in the ON clause, but *_not_* to
> t1.englmark. To me this makes no sense - if I can refer to one, I
> should be able to refer to the other?

The error is occurring because t1.englmark doesn’t exist yet at the time that the join is being processed.  It would
onlyexists after the join when the sum(case...) statements are being evaluated.  t1.class, however, is part of the
resultdatatable.
 

Your cte solution in your SQL fiddle is clean and works, so go with that.  

EXPLAIN (ANALYZE, BUFFERS) can be used to examine relative performance of different versions of the same query.

Dan
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