Github user decibel commented on the issue:
https://github.com/apache/incubator-madlib/pull/78
On 12/19/16 1:55 PM, Orhan Kislal wrote:
> We need the DISTINCT ON since there might be multiple paths with the
> same cost. The inner-most query returns a single value (using the min
> function) but the middle query might match it to multiple edges. The
> algorithm doesn't guarantee a tie-breaking clause so whatever row
> DISTINCT ON chooses should be acceptable.
Please add comments to that effect to the code.
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