swuferhong commented on code in PR #20513:
URL: https://github.com/apache/flink/pull/20513#discussion_r954730986
##########
docs/content/docs/dev/table/sql/queries/hints.md:
##########
@@ -84,4 +84,244 @@ insert into kafka_table1 /*+
OPTIONS('sink.partitioner'='round-robin') */ select
```
+## Query Hints
+
+`Query Hints` specify that the indicated hints are used in the scope of a
query. Their effective scope is current `Query
+block` ([What are query blocks ?](#what-are-query-blocks-)) which `Query
Hints` specified in. Now, Flink `Query Hints` support `Join Hints`.
+
+### Syntax
+The `Query Hints` syntax in Flink follows the syntax of `Query Hints` in
Apache Calcite:
+```sql
+# Query Hints:
+SELECT /*+ hint [, hint ] */ ...
+
+hint:
+ hintName
+ | hintName '(' optionKey '=' optionVal [, optionKey '=' optionVal ]* ')'
+ | hintName '(' hintOption [, hintOption ]* ')'
+
+optionKey:
+ simpleIdentifier
+ | stringLiteral
+
+optionVal:
+ stringLiteral
+
+hintOption:
+ simpleIdentifier
+ | numericLiteral
+ | stringLiteral
+```
+
+### Join Hints
+
+`Join Hints` allow users to suggest the join strategy to optimizer in order to
get a more optimal execution plan.
+Now Flink `Join Hints` support `BROADCAST`, `SHUFFLE_HASH`, `SHUFFLE_MERGE`
and `NEST_LOOP` Join Hints. Also, for some cases,
+`Join Hints` will conflict, we try to formulate the behavior of `Join Hints`
for these cases.
+
+*NOTE:* For all types of `Join Hints`, Flink support specifying multiple
tables in a single `Join Hint` or multiple `Join Hints` like
+`BROADCAST(t1, t2, ..., tn)` or `BROADCAST(t1), BROADCAST(t2), ...,
BROADCAST(tn)`. During query optimization, planner will
+automatically select the optimal join strategies according to the specified
`Join Hints`.
+
+#### BROADCAST
+
+{{< label Batch >}}
+
+For this type of `Join Hints`, suggests that join use `BroadCast join`
strategy. It performs well when the data volume of
+one side of table is very small. The join side with the hint will be broadcast
regardless of `table.optimizer.join.broadcast-threshold`.
+
+*NOTE:* `BROADCAST Join Hint` only supports join with equivalence join
condition. And it doesn't support `Full Outer Join`.
Review Comment:
> `BROADCAST Join Hint` -> `BROADCAST`
Done!
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