[FLINK-39616][docs] Document ORDER BY usage with FROM_CHANGELOG#28166
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| less than or equal to the watermark are delivered to the eval() method in sorted order. Late | ||
| events (arriving after the watermark) are dropped to maintain the ordering guarantee. | ||
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| This pattern is particularly useful for the built-in [`FROM_CHANGELOG`]({{< ref "docs/sql/reference/queries/changelog" >}}#from_changelog) PTF, which converts an append-only CDC stream into a changelog. Combining `PARTITION BY` on the primary key with `ORDER BY` on the event-time column reorders out-of-order CDC events per key before the operations are applied. |
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| This pattern is particularly useful for the built-in [`FROM_CHANGELOG`]({{< ref "docs/sql/reference/queries/changelog" >}}#from_changelog) PTF, which converts an append-only CDC stream into a changelog. Combining `PARTITION BY` on the primary key with `ORDER BY` on the event-time column reorders out-of-order CDC events per key before the operations are applied. | |
| This pattern is particularly useful for the built-in [`FROM_CHANGELOG`]({{< ref "docs/sql/reference/queries/changelog" >}}#from_changelog) PTF, which converts an append-only CDC stream into a changelog. Combining `PARTITION BY` on the primary key with `ORDER BY` on the event-time column reorders out-of-order CDC events per key before the conversion operations are applied. |
CDC streams often deliver events out of order. The PTF ORDER BY clause introduced in FLINK-39256 aligns naturally with FROM_CHANGELOG: partitioning by the primary key and ordering by event time reorders out-of-order CDC events per key before the operations are applied. Adds a new "Ordering CDC events with ORDER BY" subsection to the FROM_CHANGELOG documentation with the SQL example and the requirements (watermarked time attribute, ASC on the first order column, set semantics via PARTITION BY). Extends the Table API examples with the equivalent partitionBy(...).orderBy(...).fromChangelog() pattern. Adds a corresponding example in the PartitionedTable#fromChangelog Javadoc. Adds a cross-reference from the PTF ORDER BY guide to FROM_CHANGELOG so users discover the pattern from either side.
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LGTM |
featzhang
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May 16, 2026
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What is the purpose of the change
CDC streams often deliver events out of order. The PTF ORDER BY clause introduced in FLINK-39256 aligns naturally with FROM_CHANGELOG: partitioning by the primary key and ordering by event time reorders out-of-order CDC events per key before the operations are applied.
Adds a new "Ordering CDC events with ORDER BY" subsection to the FROM_CHANGELOG documentation with the SQL example and the requirements (watermarked time attribute, ASC on the first order column, set semantics via PARTITION BY). Extends the Table API examples with the equivalent partitionBy(...).orderBy(...).fromChangelog() pattern.
Adds a corresponding example in the PartitionedTable#fromChangelog Javadoc.
Adds a cross-reference from the PTF ORDER BY guide to FROM_CHANGELOG so users discover the pattern from either side.
Does this pull request potentially affect one of the following parts:
@Public(Evolving): (no)Documentation
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