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Implements https://www.pivotaltracker.com/story/show/184032869 # Important Notes - Currently we get failures in Full joins on Postgres which show a more serious problem - amending equality to ensure that `[NULL = NULL] == True` breaks hash/merge based indexing - so such joins will be extremely inefficient. All our joins currently rely on this notion of equality which will mean all of our DB joins will be extremely inefficient. - We need to find a solution that will support nulls and still work OK with indices (but after exploring a few approaches: `COALESCE(a = b, a IS NULL AND b is NULL)`, `a IS NOT DISTINCT FROM b`, `(a = b) OR (a IS NULL AND b is NULL)`; all of which did not work (they all result in `ERROR: FULL JOIN is only supported with merge-joinable or hash-joinable join conditions`) I'm less certain that it is possible. Alternatively, we may need to change the NULL semantics to align it with SQL - this seems like likely the simpler solution, allowing us to generate simple, reliable SQL - the NULL=NULL solution will be cornering us into nasty workarounds very dependent on the particular backend. |
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