mihaibudiu commented on code in PR #5132:
URL: https://github.com/apache/calcite/pull/5132#discussion_r3677691244
##########
core/src/main/java/org/apache/calcite/rel/rules/PruneEmptyRules.java:
##########
@@ -542,6 +560,30 @@ public interface SortFetchZeroRuleConfig extends
PruneEmptyRule.Config {
}
}
+ /** Configuration for a rule that prunes a Sort if its {@code OFFSET} skips
at
+ * least as many rows as its input can ever produce. */
+ @Value.Immutable
+ public interface SortOffsetGreaterThanMaxRowsRuleConfig extends
PruneEmptyRule.Config {
+ SortOffsetGreaterThanMaxRowsRuleConfig DEFAULT =
+ ImmutableSortOffsetGreaterThanMaxRowsRuleConfig.of()
+ .withOperandSupplier(b -> b.operand(Sort.class).anyInputs())
+ .withDescription("PruneSortOffsetGreaterThanMaxRows");
+
+ @Override default PruneEmptyRule toRule() {
+ return new RemoveEmptySingleRule(this) {
+ @Override public boolean matches(final RelOptRuleCall call) {
+ final Sort sort = call.rel(0);
+ // Only consider a static (non-dynamic) OFFSET. If the offset skips
at
+ // least as many rows as the input can ever produce, the Sort returns
+ // no rows. RelMdMaxRowCount#getMaxRowCount(Sort) already subtracts
the
+ // offset from the input row count, so the Sort is definitely empty.
+ return sort.offset instanceof RexLiteral
+ && RelMdUtil.isRelDefinitelyEmpty(call.getMetadataQuery(), sort);
Review Comment:
If something is definitely empty, why does it matter if it's a sort or some
other operation? Why does the offset matter?
##########
core/src/main/java/org/apache/calcite/rel/rules/PruneEmptyRules.java:
##########
@@ -231,6 +231,24 @@ private static boolean isEmpty(RelNode node) {
public static final RelOptRule SORT_FETCH_ZERO_INSTANCE =
SortFetchZeroRuleConfig.DEFAULT.toRule();
+ /**
+ * Rule that converts a {@link org.apache.calcite.rel.core.Sort}
+ * to empty if its {@code OFFSET} is greater than or equal to the maximum
+ * number of rows its input can produce, so that all rows are skipped.
+ *
+ * <p>Examples:
+ *
+ * <ul>
+ * <li>Sort[offset=5](input with at most 2 rows) becomes Empty
+ * </ul>
+ *
+ * <p>It relies on {@link org.apache.calcite.rel.metadata.RelMdMaxRowCount}
Review Comment:
How the rule is implemented should not be documented here, but in the rule
body.
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