Package org.apache.calcite.rel.rules

Class SortMergeRule

java.lang.Object
org.apache.calcite.plan.RelOptRule
org.apache.calcite.plan.RelRule<SortMergeRule.Config>
org.apache.calcite.rel.rules.SortMergeRule
All Implemented Interfaces:
TransformationRule
@Enclosing public class SortMergeRule extends RelRule<SortMergeRule.Config> implements TransformationRule
This rule try to merge the double Sort,one is Limit semantics, another sort is Limit or TOPN semantics.

It generally used with the SortProjectTransposeRule rule.

For example: 


 select
   concat('-', N_REGIONKEY) from
   (
     select
       *
     from nation limit 10000) limit 10

will convert to 


 select
   concat('-', N_REGIONKEY)
 from
   nation limit 10

The sql : 


 select concat('-',N_REGIONKEY) from
 (SELECT * FROM nation order BY N_REGIONKEY DESC LIMIT 10000) limit 10

will convert to 


 SELECT concat('-',N_REGIONKEY) FROM nation order BY N_REGIONKEY DESC LIMIT 10

In the future,we could also extend other sort merge logic in this rule.

See Also: