xiedeyantu commented on code in PR #4515:
URL: https://github.com/apache/calcite/pull/4515#discussion_r2313264165
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core/src/main/java/org/apache/calcite/rel/rules/SortJoinTransposeRule.java:
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@@ -23,25 +23,53 @@
import org.apache.calcite.rel.RelFieldCollation;
import org.apache.calcite.rel.RelNode;
import org.apache.calcite.rel.core.Join;
-import org.apache.calcite.rel.core.JoinInfo;
import org.apache.calcite.rel.core.JoinRelType;
import org.apache.calcite.rel.core.Sort;
import org.apache.calcite.rel.logical.LogicalJoin;
import org.apache.calcite.rel.logical.LogicalSort;
import org.apache.calcite.rel.metadata.RelMdUtil;
import org.apache.calcite.rel.metadata.RelMetadataQuery;
+import org.apache.calcite.rex.RexBuilder;
import org.apache.calcite.rex.RexDynamicParam;
+import org.apache.calcite.rex.RexLiteral;
+import org.apache.calcite.rex.RexNode;
import org.apache.calcite.tools.RelBuilderFactory;
+import org.checkerframework.checker.nullness.qual.Nullable;
import org.immutables.value.Value;
+import java.math.BigDecimal;
+
/**
- * Planner rule that pushes a {@link org.apache.calcite.rel.core.Sort} past a
- * {@link org.apache.calcite.rel.core.Join}.
+ * Planner rule that pushes a {@link Sort} past a {@link Join}.
+ *
+ * <p>This rule applies to left/right outer joins, and only pushes the sort if
its keys are
+ * entirely from one input. It will not fire if the sort uses dynamic
parameters or the input
+ * is already sorted and limited. However, an extension for full outer joins
for this rule could
+ * be envisioned.
*
- * <p>At the moment, we only consider left/right outer joins.
- * However, an extension for full outer joins for this rule could be
envisioned.
- * Special attention should be paid to null values for correctness issues.
+ * <p>For example, given the SQL:
+ * <pre>
+ * select d.deptno, empno from sales.dept d
+ * right join sales.emp e using (deptno) limit 10 offset 2
+ * </pre>
+ * The initial plan:
+ * <pre>
+ * LogicalProject(DEPTNO=[$0], EMPNO=[$2])
+ * LogicalSort(offset=[2], fetch=[10])
+ * LogicalJoin(condition=[=($0, $9)], joinType=[right])
+ * LogicalTableScan(table=[[CATALOG, SALES, DEPT]])
+ * LogicalTableScan(table=[[CATALOG, SALES, EMP]])
+ * </pre>
+ * After applying this rule:
+ * <pre>
+ * LogicalProject(DEPTNO=[$0], EMPNO=[$2])
+ * LogicalSort(offset=[2], fetch=[10])
+ * LogicalJoin(condition=[=($0, $9)], joinType=[right])
+ * LogicalTableScan(table=[[CATALOG, SALES, DEPT]])
+ * LogicalSort(fetch=[12])
Review Comment:
If what I said is wrong, then I don't understand why the right table must be
ordered in order to push the limit down.
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