huaxingao commented on code in PR #17822: URL: https://github.com/apache/iceberg/pull/17822#discussion_r4264447775
########## format/spec.md: ########## @@ -655,6 +658,123 @@ Sorting floating-point numbers should produce the following behavior: `-NaN` < ` A data or delete file is associated with a sort order by the sort order's id within [a manifest](#manifests). Therefore, the table must declare all the sort orders for lookup. A table could also be configured with a default sort order id, indicating how the new data should be sorted by default. Writers should use this default sort order to sort the data on write, but are not required to if the default order is prohibitively expensive, as it would be for streaming writes. +### Constraints + +Constraints are added in v4 and are not supported in v3 or earlier. + +A **constraint** declares a condition that a table's rows are expected to satisfy. Its definition is stored in table metadata. Each snapshot contains the writer-reported status of each constraint that existed when the snapshot was created; see [Constraint Validation](#constraint-validation). + +Three constraint types are defined: + +* `check` -- every row must satisfy a predicate +* `unique` -- the values of a set of fields must be distinct across the rows in which every field in the set is non-null; a row in which any field in the set is null is not compared, so more than one such row may exist +* `primary-key` -- the values of a set of fields must be distinct across all rows and must not be null + +A constraint is stored separately from the table schema and must refer to fields by field ID. Constraints may evolve independently from the schema, being added, modified, or removed. + +#### Constraint Fields + +A constraint consists of the following fields: + +| Requirement | Field name | Type | Description | +|-------------|---------------------------|-----------|-------------| +| _required_ | **`constraint-id`** | `int` | ID of the constraint; unique within the table | +| _required_ | **`type`** | `string` | The constraint type: `check`, `unique`, or `primary-key` | +| _required_ | **`name`** | `string` | A name for the constraint that is unique within the table. Names are for human consumption and must not be used to identify a constraint in metadata | +| _required_ | **`enforced`** | `boolean` | Whether writers must only add rows that satisfy the constraint | +| _required_ | **`timestamp-ms`** | `long` | Timestamp in milliseconds from the unix epoch when the constraint was created or last modified. The timestamp is informational and must not be used to determine whether a constraint applies to a snapshot or whether it holds | +| _optional_ | **`expression`** | `expression` | The predicate that every row must satisfy, see [Check Constraint Expressions](#check-constraint-expressions). Required for a `check` constraint and must not be set for other types | +| _optional_ | **`field-ids`** | `list<int>` | The list of field IDs that the constraint applies to. Required for a `unique` or `primary-key` constraint and must not be set for a `check` constraint | + +The fields that define what a constraint requires are embedded directly in the constraint based on its `type`. Each type carries only the metadata that it requires: a `check` constraint has an `expression` and must not declare `field-ids`, and a `unique` or `primary-key` constraint has `field-ids` and must not declare an `expression`. This keeps a single source of truth for the fields that a constraint references. + +The `field-ids` of a `unique` or `primary-key` constraint must reference primitive fields and must not reference fields within a `list` or a `map`. Fields of type `float`, `double`, `geometry`, or `geography` must not be used because Iceberg does not define equality for them. Fields of type `unknown` must not be used because their values are always null. + +The fields of a `primary-key` constraint must be `required` and must not be nested in an optional struct, so that the schema rules out null keys even when the constraint is not enforced. These are the same restrictions that apply to [identifier fields](#identifier-field-ids). The fields of a `unique` constraint may be optional or nested in optional structs, because a row in which any field is null is not compared. + +When a constraint is `enforced`, writers must only add rows they can prove follow the constraint. A constraint that is not enforced can be written to by any writer, regardless of their ability to prove that the constraint is followed by new rows. Review Comment: Good catch. I added a sentence: a changed row counts as a removed row and an added row, whether the engine models it as delete and insert or as a modification that keeps the row ID. So the rules give the same answer either way. ########## format/spec.md: ########## @@ -655,6 +658,123 @@ Sorting floating-point numbers should produce the following behavior: `-NaN` < ` A data or delete file is associated with a sort order by the sort order's id within [a manifest](#manifests). Therefore, the table must declare all the sort orders for lookup. A table could also be configured with a default sort order id, indicating how the new data should be sorted by default. Writers should use this default sort order to sort the data on write, but are not required to if the default order is prohibitively expensive, as it would be for streaming writes. +### Constraints + +Constraints are added in v4 and are not supported in v3 or earlier. + +A **constraint** declares a condition that a table's rows are expected to satisfy. Its definition is stored in table metadata. Each snapshot contains the writer-reported status of each constraint that existed when the snapshot was created; see [Constraint Validation](#constraint-validation). + +Three constraint types are defined: + +* `check` -- every row must satisfy a predicate +* `unique` -- the values of a set of fields must be distinct across the rows in which every field in the set is non-null; a row in which any field in the set is null is not compared, so more than one such row may exist +* `primary-key` -- the values of a set of fields must be distinct across all rows and must not be null + +A constraint is stored separately from the table schema and must refer to fields by field ID. Constraints may evolve independently from the schema, being added, modified, or removed. + +#### Constraint Fields + +A constraint consists of the following fields: + +| Requirement | Field name | Type | Description | +|-------------|---------------------------|-----------|-------------| +| _required_ | **`constraint-id`** | `int` | ID of the constraint; unique within the table | +| _required_ | **`type`** | `string` | The constraint type: `check`, `unique`, or `primary-key` | +| _required_ | **`name`** | `string` | A name for the constraint that is unique within the table. Names are for human consumption and must not be used to identify a constraint in metadata | +| _required_ | **`enforced`** | `boolean` | Whether writers must only add rows that satisfy the constraint | +| _required_ | **`timestamp-ms`** | `long` | Timestamp in milliseconds from the unix epoch when the constraint was created or last modified. The timestamp is informational and must not be used to determine whether a constraint applies to a snapshot or whether it holds | +| _optional_ | **`expression`** | `expression` | The predicate that every row must satisfy, see [Check Constraint Expressions](#check-constraint-expressions). Required for a `check` constraint and must not be set for other types | +| _optional_ | **`field-ids`** | `list<int>` | The list of field IDs that the constraint applies to. Required for a `unique` or `primary-key` constraint and must not be set for a `check` constraint | Review Comment: Good point. Changed to "set". -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. 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