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https://issues.apache.org/jira/browse/CALCITE-4223?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17205961#comment-17205961
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Julian Hyde commented on CALCITE-4223:
--------------------------------------
I started writing a PR, but there is already a perfect example. In CALCITE-1861
I wanted a table to be able to declare its own predicates. So I added 4 lines
to {{getAllPredicates}}:
{code}
public RelOptPredicateList getAllPredicates(TableScan scan, RelMetadataQuery
mq) {
final BuiltInMetadata.AllPredicates.Handler handler =
scan.getTable().unwrap(BuiltInMetadata.AllPredicates.Handler.class);
if (handler != null) {
return handler.getAllPredicates(scan, mq);
}
return RelOptPredicateList.EMPTY;
}
{code}
and I made a mock table that called {{addWrap}} to add its own implementation
of {{AllPredicates.Handler}}:
{code}
restaurantTable.addWrap(
new BuiltInMetadata.AllPredicates.Handler() {
public RelOptPredicateList getAllPredicates(RelNode r,
RelMetadataQuery mq) {
...
}
});
{code}
Put a break-point in {{RelMdAllPredicates.getAllPredicates(TableScan scan,
RelMetadataQuery mq)}} and run {{RelOptRulesTest.testSpatialDWithinToHilbert}}
and see how your break-point gets hit.
We need to check for handlers in all {{RelMdXxx.getXxx(TableScan,
RelMdataQuery)}} methods. If I did it again I'd implement {{interface
AllPredicates}} rather than {{interface AllPredicates.Handler}}, but the
principle is the same.
> Introducing column statistics to RelOptTable
> --------------------------------------------
>
> Key: CALCITE-4223
> URL: https://issues.apache.org/jira/browse/CALCITE-4223
> Project: Calcite
> Issue Type: Improvement
> Reporter: Chunwei Lei
> Assignee: Chunwei Lei
> Priority: Major
> Labels: pull-request-available
> Time Spent: 40m
> Remaining Estimate: 0h
>
> Many systems depend on column statistics to compute more accurate stats, such
> as NDV, average column size, and so on. It would be nice if Calcite can
> provide such an interface.
> Column statistics might include NDV, average/max column length, number of
> nulls, number of trues, number of falses and so on.
> What do you think?
>
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