Package org.apache.calcite.rel.rules

Class SortRemoveRedundantRule

java.lang.Object
org.apache.calcite.plan.RelOptRule
org.apache.calcite.plan.RelRule<SortRemoveRedundantRule.Config>
org.apache.calcite.rel.rules.SortRemoveRedundantRule
All Implemented Interfaces:
TransformationRule
@Enclosing public class SortRemoveRedundantRule extends RelRule<SortRemoveRedundantRule.Config> implements TransformationRule
Rule that removes redundant ORDER BY or LIMIT when its input RelNode's maximum row count is less than or equal to specified row count. All of them are represented by Sort.

If a Sort is an ORDER BY with no OFFSET, and if input's maximum row count is less than or equal to 1, then the sort is redundant (because every relation with 1 or fewer rows is sorted), and the rule removes the redundant sort.

For example: 


 SELECT max(totalprice)
 FROM orders
 ORDER BY 1

could be converted to 


 SELECT max(totalprice)
 FROM orders

For example: 


 SELECT count(*)
 FROM orders
 ORDER BY 1 LIMIT 10

could be converted to 


 SELECT count(*)
 FROM orders

If a Sort is a pure LIMIT (with no ORDER BY or OFFSET), and its input RelNode's maximum row count is less than or equal to the limit's fetch, the rule removes the redundant LIMIT.

For example: 


 SELECT *
 FROM (VALUES 1, 2, 3, 4, 5, 6) AS t1
 LIMIT 10

The above VALUES row count is 6 rows, and the limit's fetch is 10, so we could remove the redundant sort.

It could be converted to: 


 SELECT * FROM (VALUES 1,2,3,4,5,6) AS t1
See Also: