laurentgo commented on code in PR #13879:
URL: https://github.com/apache/iceberg/pull/13879#discussion_r2467807774
##########
open-api/rest-catalog-open-api.yaml:
##########
@@ -3260,6 +3260,71 @@ components:
additionalProperties:
type: string
+ ReadRestrictions:
+ type: object
+ description: >
+ Read restrictions for a table, including projection and row filter
expressions, according to the current schema.
+
+ A client MUST enforce the restrictions defined in this object when
reading data
+ from the table.
+
+ These restrictions apply only to the authenticated principal, user,
or account
+ associated with the client. They MUST NOT be interpreted as global
policy and
+ MUST NOT be applied beyond the entity identified by the
Authentication header
+ (or other applicable authentication mechanism).
+ properties:
+ required-projection:
+ description: >
+ A list of projections that MUST be applied prior to any
query-specified
+ projections.
+ If the required-projection property is absent or empty, no
mandatory projection applies,
+ and a reader MAY project any subset of columns of the table,
including all columns.
+
+ 1. A reader MUST project only columns listed in the
required-projection.
+ - If a listed column has a transform, the reader MUST apply it
and replace
+ all references to the underlying column with the transformed
value
+ (for example, truncate(4, cc) MUST be projected as truncate(4,
cc) AS cc,
+ and all references to cc during query evaluation MUST resolve
to this alias).
+ - If a listed column has no transform, the reader MUST read it
as-is.
+ - Columns not listed in the required-projection MUST NOT be read.
+
+ 2. A column MUST appear at most once in the required-projection.
+
+ 3. A projection entry MUST reference either the column itself or
exactly one
+ transformed version of the column, but not both.
+
+ 4. Multiple transformed versions of the same column (e.g.,
truncate(5, col)
Review Comment:
I guess it's a consequence of not having explicit mapping between a column
and the transformation. Assuming that the mapping was explicit, it should be
possible to have the same expression `truncate(3, col1)` applied to `col1` and
`col2` columns. The previous example may not seem very useful but:
1/ the table could have some fallback column containing safe data to use as
a replacement for multiple columns
2/ the transformation would be a UDF which would need multiple columns as
their input for example
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