xiedeyantu commented on code in PR #4566:
URL: https://github.com/apache/calcite/pull/4566#discussion_r2401190551
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core/src/main/java/org/apache/calcite/rel/metadata/BuiltInMetadata.java:
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@@ -901,21 +901,70 @@ default RelDataTypeFactory getTypeFactory() {
}
}
- /** Metadata about the functional dependency of columns. */
+ /** Metadata about the functional dependency of column ordinals. */
public interface FunctionalDependency extends Metadata {
MetadataDef<FunctionalDependency> DEF =
MetadataDef.of(FunctionalDependency.class,
FunctionalDependency.Handler.class,
- BuiltInMethod.FUNCTIONAL_DEPENDENCY.method);
+ BuiltInMethod.FUNCTIONAL_DEPENDENCY.method,
+ BuiltInMethod.FUNCTIONAL_DEPENDENCY_SET.method,
+ BuiltInMethod.FUNCTIONAL_DEPENDENCY_CLOSURE.method,
+
BuiltInMethod.FUNCTIONAL_DEPENDENCY_CANDIDATE_KEYS_OR_SUPER_KEYS.method);
/**
- * Returns whether column is functionally dependent on column.
+ * Returns whether column ordinal {@code determinant} functionally
determines
+ * column ordinal {@code dependent}.
+ *
+ * @param determinant 0-based ordinal of determinant column
+ * @param dependent 0-based ordinal of dependent column
+ * @return {@code true} if determinant uniquely determines dependent;
+ * {@code false} if not;
+ * {@code null} if unknown
*/
- @Nullable Boolean determines(int key, int column);
+ @Nullable Boolean determines(int determinant, int dependent);
+
+ /**
+ * Returns whether column ordinals in {@code determinants} functionally
determine
+ * column ordinals in {@code dependents}.
+ *
+ * @param determinants 0-based ordinals of determinant columns
+ * @param dependents 0-based ordinals of dependent columns
+ * @return true if determinants uniquely determine dependents
+ */
+ Boolean determinesSet(ImmutableBitSet determinants, ImmutableBitSet
dependents);
+
+ /**
+ * Returns the closure of {@code ordinals} under the functional dependency
set.
+ * The closure is the set of column ordinals uniquely determined by {@code
ordinals}.
+ *
+ * @param ordinals 0-based ordinals of determinant columns
+ * @return closure: columns functionally determined by {@code ordinals}
+ */
+ ImmutableBitSet computeClosure(ImmutableBitSet ordinals);
+
+ /**
+ * Finds candidate keys or superkeys in {@code ordinals} under the
functional dependency set.
Review Comment:
> If a table contains duplicates then NOTHING we know about functional
dependencies will allow us to deduce keys. (To fix this, you could introduce a
special attribute that represents row-identity.)
I think this point can be interpreted more broadly. As long as a value in
col1 can uniquely determine a value in col2, we should consider that col1 →
col2 holds.
For example:
((1, 'a'), (1, 'a'), (2, 'b')) as (col1, col2)
In this case, I believe this dependency is acceptable:
Value 1 in col1 always determines value 'a' in col2
Value 2 in col1 always determines value 'b' in col2
Therefore, the functional dependency col1 → col2 should be considered valid.
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