Interface RelMetadataProvider

    • Method Detail

      • apply

        <M extends MetadataUnboundMetadata<M> apply​(java.lang.Class<? extends RelNode> relClass,
                                                      java.lang.Class<? extends M> metadataClass)
        Retrieves metadata of a particular type and for a particular sub-class of relational expression.

        The object returned is a function. It can be applied to a relational expression of the given type to create a metadata object.

        For example, you might call

         RelMetadataProvider provider;
         LogicalFilter filter;
         RexNode predicate;
         Function<RelNode, Metadata> function =
           provider.apply(LogicalFilter.class, Selectivity.class};
         Selectivity selectivity = function.apply(filter);
         Double d = selectivity.selectivity(predicate);
        relClass - Type of relational expression
        metadataClass - Type of metadata
        Function that will field a metadata instance; or null if this provider cannot supply metadata of this type