rdblue commented on a change in pull request #3556:
URL: https://github.com/apache/iceberg/pull/3556#discussion_r749715445
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File path: site/docs/spec.md
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@@ -212,6 +212,9 @@ Columns in Iceberg data files are selected by field id. The
table schema's colum
For example, a file may be written with schema `1: a int, 2: b string, 3: c
double` and read using projection schema `3: measurement, 2: name, 4: a`. This
must select file columns `c` (renamed to `measurement`), `b` (now called
`name`), and a column of `null` values called `a`; in that order.
+Tables may also define a property `schema.name-mapping.default` with a JSON
map of `columnName` -> `fieldId` which will be used if a data file was written
without field ids. This `NameMapping` will **only** be used on files without
field ids. Files imported or added to an Iceberg table from a system that does
not generate field ids will fall back to using the table's name mapping to map
columns to field ids.
Review comment:
Oh, and if name does contain `.`, then the field name itself must
contain `.`. A mapping for `names: ["a.b"]` will map a field called `"a.b"` and
does NOT apply to field `"b"` nested within a field `"a"`.
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