LakeShen commented on code in PR #3345:
URL: https://github.com/apache/calcite/pull/3345#discussion_r1285763589
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core/src/main/java/org/apache/calcite/rel/metadata/BuiltInMetadata.java:
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@@ -105,6 +106,43 @@ interface Handler extends MetadataHandler<UniqueKeys> {
}
}
+ /**
+ * Metadata about which columns have foreign keys.
+ */
+ public interface ForeignKeys extends Metadata {
+ MetadataDef<ForeignKeys> DEF =
+ MetadataDef.of(ForeignKeys.class, ForeignKeys.Handler.class,
+ BuiltInMethod.FOREIGN_KEYS.method);
+
+ /**
+ * Extract foreign keys from {@link org.apache.calcite.rel.RelNode}.
+ * Foreign keys are represented as an {@link
org.apache.calcite.util.ImmutableBitSet},
+ * where each bit position represents a 0-based output column ordinal.
+ *
+ * @param ignoreNulls if true, allow containing null values when
determining
+ * whether the keys are foreign keys
+ *
+ * @return bit set of foreign keys(contains intermediate inferred foreign
keys),
+ * or empty if not enough information is available to make that
determination
+ */
+ Set<RelOptForeignKey> getForeignKeys(boolean ignoreNulls);
Review Comment:
Is it @Nullable ? Like this method:
```sql
@Nullable Set<ImmutableBitSet> getUniqueKeys(boolean ignoreNulls);
```
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