Refine join parsing #111
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Refine join parsing #111
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Pull Request Test Coverage Report for Build 348
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nickolay
approved these changes
Jun 13, 2019
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Hey @benesch, thanks for extracting this into its own PR!
As promised, after thinking about it I agree with your approach -- while it seems this could be theoretically parsed without backtracking, it would significantly complicate the code in exchange for being more efficient when parsing nested joins, which I expect to be quite rare.
I had some suggestions, which I pushed as separate commits here, to be squashed with existing ones, if you agree with the changes.
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Yeah, the new commits look great! I'll squash and merge in just a moment. |
This commit adds support for derived tables (i.e., subqueries) that
incorporate set operations, like:
SELECT * FROM (((SELECT 1) UNION (SELECT 2)) t1 AS NATURAL JOIN t2)
This introduces a bit of complexity around determining whether a left
paren starts a subquery, starts a nested join, or belongs to an
already-started subquery. The details are explained in a comment within
the patch.
The SQL specification prohibits constructions like
SELECT * FROM a NATURAL JOIN (b)
where b sits alone inside parentheses. Parentheses in a FROM entry
always introduce either a derived table or a join.
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Additional join tweaks for better compliance with the standard. Extracted from #109.
@nickolay no rush at all on this! I'm not currently in need of the changes here, but I wanted to cross the i's and dot the t's while the code was fresh in my mind.