julianhyde commented on code in PR #2916:
URL: https://github.com/apache/calcite/pull/2916#discussion_r976851396
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core/src/main/java/org/apache/calcite/rel/rules/PruneEmptyRules.java:
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@@ -480,9 +486,25 @@ public interface JoinLeftEmptyRuleConfig extends
PruneEmptyRule.Config {
return new PruneEmptyRule(this) {
@Override public void onMatch(RelOptRuleCall call) {
Join join = call.rel(0);
+ Values empty = call.rel(1);
+ RelNode right = call.rel(2);
+ RexBuilder rexBuilder = call.builder().getRexBuilder();
if (join.getJoinType().generatesNullsOnLeft()) {
// "select * from emp right join dept" is not necessarily empty if
// emp is empty
+ // join can be removed and take the right branch, all columns come
from emp are null
+ List<RexNode> projects = new ArrayList<>(
+ empty.getRowType().getFieldCount() +
right.getRowType().getFieldCount());
+ List<String> columnNames = new ArrayList<>(
+ empty.getRowType().getFieldCount() +
right.getRowType().getFieldCount());
+ // left
+ addNullLiterals(rexBuilder, empty, projects, columnNames);
+ // right
+ copyProjects(rexBuilder, right.getRowType(),
+ join.getRowType(), empty.getRowType().getFieldCount(),
projects, columnNames);
+
+ RelNode project = call.builder().push(right).project(projects,
columnNames).build();
+ call.transformTo(project);
Review Comment:
Can this be written in a functional style? Rather than creating empty lists
then filling them, use `map`. `RelBuilder` has plenty of methods that return
lists to types, lists of names, etc.
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