rdblue commented on a change in pull request #4301:
URL: https://github.com/apache/iceberg/pull/4301#discussion_r823219803
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File path: format/spec.md
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@@ -193,10 +193,38 @@ Notes:
For details on how to serialize a schema to JSON, see Appendix C.
+#### Default value
+Default values can be assigned to top-level columns or nested fields. Default
values are used during schema evolution when adding a new column. The default
value is used to read rows belonging to the files that lack the column or
nested field prior to the schema evolution.
Review comment:
This just occurred to me and I want to note it somewhere: right now we
assume that missing columns are null in a lot of places. We'll need to be
careful about the implementation and make sure we catch things like Parquet
file filters that assume a missing column is null.
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