Github user bitblender commented on a diff in the pull request:
https://github.com/apache/drill/pull/837#discussion_r122287615
--- Diff:
exec/java-exec/src/main/java/org/apache/drill/exec/record/BatchSchema.java ---
@@ -162,20 +162,22 @@ private boolean majorTypeEqual(MajorType t1,
MajorType t2) {
* Merge two schema to produce a new, merged schema. The caller is
responsible
* for ensuring that column names are unique. The order of the fields in
the
* new schema is the same as that of this schema, with the other
schema's fields
- * appended in the order defined in the other schema. The resulting
selection
- * vector mode is the same as this schema. (That is, this schema is
assumed to
- * be the main part of the batch, possibly with a selection vector, with
the
- * other schema representing additional, new columns.)
+ * appended in the order defined in the other schema.
+ * <p>
+ * Merging data with selection vectors is unlikely to be useful, or work
well.
--- End diff --
Can you please leave a comment about why this is unlikely to be useful, or
work well?
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