citusdata / pg_shard / 42

36%

Pull #54

travis-ci

Fix multi-shard SELECT to pull only needed columns

Adds a new test to verify that the remote SQL generated during a multi-
shard SELECT contains only columns needed for the local portion of
query execution. Previously, columns referenced by WHERE clauses would
always be pulled because the local portion of execution retained the
WHERE quals from the original query. Now the remote query leaves those
columns empty unless they are referenced by an aggregate, GROUP BY,
ORDER BY, or directly in the target list. To make this new approach
work, we partition quals into remote and local lists and then send the
remote and local queries with their respective lists.

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