Reduce indentation/parenthesization of set operations in rule/view dumps

Enterprise / PostgreSQL - Tom Lane [sss.pgh.pa.us] - 30 April 2014 12:26 UTC

A query such as "SELECT x UNION SELECT y UNION SELECT z UNION ..." produces a left-deep nested parse tree, which we formerly showed in its full nested glory and with all the possible parentheses. This does little for readability, though, and long UNION lists resulting in excessive indentation are common. Instead, let's omit parentheses and indent all the subqueries at the same level in such cases.

This patch skips indentation/parenthesization whenever the lefthand input of a SetOperationStmt is another SetOperationStmt of the same kind and ALL/DISTINCT property. We could teach the code the exact syntactic precedence of set operations and thereby avoid parenthesization in some more cases, but it's not clear that that'd be a readability win: it seems better to parenthesize if the set operation changes. (As an example, if there's one UNION in a long list of UNION ALL, it now stands out like a sore thumb, which seems like a good thing.)

Back-patch to 9.3. This completes our response to a complaint from Greg Stark that since commit 62e666400d there's a performance problem in pg_dump for views containing long UNION sequences (or other types of deeply nested constructs). The previous commit 0601cb54dac14d979d726ab2ebeda251ae36e857 handles the general problem, but this one makes the specific case of UNION lists look a lot nicer.

41de93c Reduce indentation/parenthesization of set operations in rule/view dumps.
src/backend/utils/adt/ruleutils.c | 81 +++++---
src/test/regress/expected/create_view.out | 274 +++++++++++++--------------
src/test/regress/expected/matview.out | 24 +--
src/test/regress/expected/rules.out | 290 ++++++++++++++---------------
src/test/regress/expected/with.out | 84 ++++-----
5 files changed, 390 insertions(+), 363 deletions(-)

Upstream: git.postgresql.org

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