godfreyhe commented on code in PR #20118:
URL: https://github.com/apache/flink/pull/20118#discussion_r915444008
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flink-table/flink-table-planner/src/main/java/org/apache/flink/table/planner/plan/rules/logical/PushProjectIntoTableSourceScanRule.java:
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@@ -337,11 +339,71 @@ private RowType performPushDown(
private List<RexNode> rewriteProjections(
RelOptRuleCall call, TableSourceTable source, NestedSchema
projectedSchema) {
final LogicalProject project = call.rel(0);
+ List<RexNode> newProjects = project.getProjects();
+
if (supportsProjectionPushDown(source.tableSource())) {
- return NestedProjectionUtil.rewrite(
- project.getProjects(), projectedSchema,
call.builder().getRexBuilder());
- } else {
- return project.getProjects();
+ // if support project push down, then all input ref will be
rewritten includes metadata
+ // columns.
+ newProjects =
+ NestedProjectionUtil.rewrite(
+ newProjects, projectedSchema,
call.builder().getRexBuilder());
+ } else if (supportsMetadata(source.tableSource())) {
+ // supportsMetadataProjection only.
+ // Note: why not reuse the NestedProjectionUtil to rewrite
metadata projection? because
+ // it only works for sources which support projection push down.
+ List<Column.MetadataColumn> metadataColumns =
+ DynamicSourceUtils.extractMetadataColumns(
+ source.contextResolvedTable().getResolvedSchema());
+ if (metadataColumns.size() > 0) {
+ Set<String> metaCols =
+ metadataColumns.stream().map(m ->
m.getName()).collect(Collectors.toSet());
+
+ MetadataOnlyProjectionRewriter rewriter =
+ new MetadataOnlyProjectionRewriter(
+ project.getInput().getRowType(),
source.getRowType(), metaCols);
+
+ newProjects =
+ newProjects.stream()
+ .map(p -> p.accept(rewriter))
+ .collect(Collectors.toList());
+ }
+ }
+
+ return newProjects;
+ }
+
+ private class MetadataOnlyProjectionRewriter extends RexShuttle {
Review Comment:
nit: This class can be marked as `static`
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