KurtYoung commented on a change in pull request #8051: [FLINK-12018]
[table-planner-blink] Add support for generating optimized logical plan for
Sort and Rank
URL: https://github.com/apache/flink/pull/8051#discussion_r270618484
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File path:
flink-table/flink-table-planner-blink/src/main/scala/org/apache/flink/table/plan/nodes/calcite/Rank.scala
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@@ -34,44 +34,42 @@ import java.util
import scala.collection.JavaConversions._
/**
- * Relational expression that returns the rows in which the rank function
value of each row
+ * Relational expression that returns the rows in which the rank number of
each row
* is in the given range.
*
- * <p>NOTES: Different from
[[org.apache.calcite.sql.fun.SqlStdOperatorTable.RANK]],
- * [[Rank]] is a Relational expression， not a window function.
+ * The node is an optimization of `OVER` for some special cases,
+ * e.g.
+ * {{{
+ * SELECT * FROM (
+ * SELECT a, b, RANK() OVER (PARTITION BY b ORDER BY c) rk FROM MyTable) t
+ * WHERE rk < 10
+ * }}}
+ * can be converted to this node.
*
- * <p>[[Rank]] will output rank function value as its last column.
- *
- * <p>This RelNode only handles single rank function, is an optimization for
some cases. e.g.
- * <ol>
- * <li>
- * single rank function (on `OVER`) with filter in a SQL query statement
- * </li>
- * <li>
- * `ORDER BY` with `LIMIT` in a SQL query statement
- * (equivalent to `ROW_NUMBER` with filter and project)
- * </li>
- * </ol>
- *
- * @param cluster cluster that this relational expression belongs to
- * @param traitSet the traits of this rel
- * @param input input relational expression
- * @param rankFunction rank function, including: CUME_DIST, DENSE_RANK,
PERCENT_RANK, RANK,
- * ROW_NUMBER
- * @param partitionKey partition keys (may be empty)
- * @param sortCollation order keys for rank function
- * @param rankRange the expected range of rank function value
+ * @param cluster cluster that this relational expression belongs to
+ * @param traitSet the traits of this rel
+ * @param input input relational expression
+ * @param partitionKey partition keys (may be empty)
Review comment:
Can this be empty?
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