wmoustafa commented on a change in pull request #4301:
URL: https://github.com/apache/iceberg/pull/4301#discussion_r840966283
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File path: format/spec.md
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@@ -193,6 +193,17 @@ Notes:
For details on how to serialize a schema to JSON, see Appendix C.
+#### Default value
+
+Default value can be assigned to a column when the column is added to an
Iceberg table as part of the schema evolution. They are tracked at the level of
a nested field inside a struct, thus it can be used for both top-level columns
and nested columns. Iceberg tracks two default values internally:
`initial-default` and `write-default`. The `initial-default` is used to read
rows belonging to files that lack the column (i.e. the files were written
before the column is added); the `write-default` value will be used for the
automatically populating the column if user later inserts new rows without
specifying the column.
Review comment:
@rdblue I am fine with that. Could you comment on the intro (the second
paragraph in my comment)?
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