for writeAllChanges, if there are only match clauses, you choose "rightOuter" , I think you should use "inner join",but why not?

val joinType = if (shouldOptimizeMatchedOnlyMerge(spark)) {
      "rightOuter"
    } else {
      "fullOuter"
    }

merge is operating at the file level... if you do an inner join here, you'll effectively delete all the rows that didn't match, even though they should persist aka. we rewrite the rows that evaluate to a no-op