xuzifu666 commented on code in PR #5132:
URL: https://github.com/apache/calcite/pull/5132#discussion_r3687411060
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core/src/main/java/org/apache/calcite/rel/rules/PruneEmptyRules.java:
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@@ -525,20 +541,20 @@ public interface IntersectEmptyPruneRuleConfig extends
PruneEmptyRule.Config {
}
}
- /** Configuration for a rule that prunes a Sort if it has limit 0. */
+ /** Configuration for a rule that prunes a Sort if it is definitely empty,
+ * for example because its input is empty, it has {@code LIMIT 0}, or its
+ * {@code OFFSET} skips more rows than the input can produce. */
@Value.Immutable
- public interface SortFetchZeroRuleConfig extends PruneEmptyRule.Config {
- SortFetchZeroRuleConfig DEFAULT = ImmutableSortFetchZeroRuleConfig.of()
+ public interface SortEmptyRuleConfig extends PruneEmptyRule.Config {
+ SortEmptyRuleConfig DEFAULT = ImmutableSortEmptyRuleConfig.of()
.withOperandSupplier(b -> b.operand(Sort.class).anyInputs())
- .withDescription("PruneSortLimit0");
+ .withDescription("PruneSortIfEmpty");
@Override default PruneEmptyRule toRule() {
return new RemoveEmptySingleRule(this) {
@Override public boolean matches(final RelOptRuleCall call) {
- Sort sort = call.rel(0);
- return sort.fetch != null
- && !(sort.fetch instanceof RexDynamicParam)
- &&
RexLiteral.bigDecimalValue(sort.fetch).equals(BigDecimal.ZERO);
+ final Sort sort = call.rel(0);
Review Comment:
You're right that `isRelDefinitelyEmpty` itself is generic.
The reason this rule is specific to Sort is that the replacement logic is
not generic: `RemoveEmptySingleRule` can safely turn any `SingleRel` into an
empty Values, but Join, Union, Intersect, Minus, and Aggregate each need their
own logic when they are empty. This rule reuses RemoveEmptySingleRule because
Sort is a SingleRel. A fully generic prune anything that is definitely empty
rule would need a way to know how to rewrite each operator type correctly. The
existing EMPTY_TABLE_INSTANCE follows the same pattern: it uses
isRelDefinitelyEmpty but only for TableScan.
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