Gian Merlino ca6053d045 SQL: Resolve column type conflicts in favor of newer segments. (#3930)
* SQL: Resolve column type conflicts in favor of newer segments.

Helps with schema evolution from e.g. long -> float, which is supported
on the query side.

* Take columns from highest timestamp instead of max segment id.

* Fixes and docs.
2017-02-15 17:48:49 -08:00
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