Whatsonyourmind commented on issue #21310:
URL: https://github.com/apache/datafusion/issues/21310#issuecomment-4250137806

   @asolimando You're right to push back — I overstated it. PostgreSQL does not 
have a dedicated UNION-to-OR rewriter. What I was thinking of is the 
combination of Append node flattening and constraint exclusion 
(`constraint_exclusion`) that can prune unnecessary branches at plan time, but 
that's not the same thing as rewriting UNION into OR predicates. I should have 
been more precise rather than citing a mechanism that doesn't exist in that 
form.
   
   The point about skipping the rewrite when either branch contains LIMIT 
stands on its own merits regardless — the non-determinism argument doesn't 
depend on a PostgreSQL precedent.
   
   Thanks for catching that.


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