davidradl commented on code in PR #28737:
URL: https://github.com/apache/flink/pull/28737#discussion_r3585782418
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docs/content/docs/sql/reference/queries/joins.md:
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@@ -300,6 +300,74 @@ The main difference between above Temporal Table DDL and
Temporal Table Function
- The temporal table DDL can be defined in SQL but temporal table function can
not;
- Both temporal table DDL and temporal table function support temporal join
versioned table, but only temporal table function can temporal join the latest
version of any table/view.
+LATERAL SNAPSHOT Join
+--------------
+
+{{< label Streaming >}}
+
+A `LATERAL SNAPSHOT` join is a *stream enrichment* join that augments an
append-only table (the *probe* side) with the current state of an updating
table (the *build* side).
+Unlike an [event-time temporal join](#event-time-temporal-join), it does not
correlate each probe-side row with a specific historical version of the build
side.
+Instead, every probe-side row is joined with the build-side state that is
current at the time the row is processed, similar to a [processing-time
temporal join](#processing-time-temporal-join), but with well-defined behavior
at query start-up.
+
+The `LATERAL SNAPSHOT` join is designed for scenarios where the other temporal
joins are a poor fit:
+
+- The build side updates **infrequently**. An event-time temporal join relies
on continuous build-side watermarks to emit results, so a build side that
rarely advances its watermark stalls the join and lets probe-side state
accumulate. A `LATERAL SNAPSHOT` join does not stall when the build side goes
idle.
+- The application has **low-latency** requirements that are incompatible with
the watermark-induced delay of an event-time temporal join.
+- The build side has **no primary key**. Event-time and processing-time
temporal joins require the build-side primary key to appear in the equi-join
condition; a `LATERAL SNAPSHOT` join does not.
Review Comment:
does this mean the probe side has a primary key?
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