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    • Tom Lane's avatar
      Make reduce_outer_joins() smarter about semijoins. · 9688c4e6
      Tom Lane authored
      reduce_outer_joins() mistakenly treated a semijoin like a left join for
      purposes of deciding whether not-null constraints created by the join's
      quals could be passed down into the join's left-hand side (possibly
      resulting in outer-join simplification there).  Actually, semijoin works
      like inner join for this purpose, ie, we do not need to see any rows that
      can't possibly satisfy the quals.  Hence, two-line fix to treat semi and
      inner joins alike.  Per observation by Andres Freund about a performance
      gripe from Yazan Suleiman.
      
      Back-patch to 8.4, since this oversight has been there since the current
      handling of semijoins was implemented.
      9688c4e6
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