rdblue commented on a change in pull request #4301:
URL: https://github.com/apache/iceberg/pull/4301#discussion_r824286886
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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:
> The default value can be changed without any consequences (even
considering 1 was the schema evolution one)
@wmoustafa, this is why changing the schema evolution default is allowed as
an incompatible change through the API. Mistakes happen and we can allow
correcting them (for example, a typo of `DEFAULT 12` instead of `DEFAULT 1`).
We just can't allow the default from when the column is added to change through
a `SET DEFAULT` command.
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