core/src/main/java/org/apache/calcite/schema/Statistics.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to you under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.calcite.schema;

import org.apache.calcite.rel.RelCollation;
import org.apache.calcite.rel.RelDistribution;
import org.apache.calcite.rel.RelDistributionTraitDef;
import org.apache.calcite.util.ImmutableBitSet;

import com.google.common.collect.ImmutableList;

import java.util.List;

/**
 * Utility functions regarding {@link Statistic}.
 */
public class Statistics {
  private Statistics() {
  }

  /** Returns a {@link Statistic} that knows nothing about a table. */
  public static final Statistic UNKNOWN =
      new Statistic() {
        public Double getRowCount() {
          return null;
        }

        public boolean isKey(ImmutableBitSet columns) {
          return false;
        }

        public List<RelCollation> getCollations() {
          return ImmutableList.of();
        }

        public RelDistribution getDistribution() {
          return RelDistributionTraitDef.INSTANCE.getDefault();
        }
      };

  /** Returns a statistic with a given row count and set of unique keys. */
  public static Statistic of(final double rowCount,
      final List<ImmutableBitSet> keys) {
    return of(rowCount, keys, ImmutableList.<RelCollation>of());
  }

  /** Returns a statistic with a given row count and set of unique keys. */
  public static Statistic of(final double rowCount,
      final List<ImmutableBitSet> keys, final List<RelCollation> collations) {
    return new Statistic() {
      public Double getRowCount() {
        return rowCount;
      }

      public boolean isKey(ImmutableBitSet columns) {
        for (ImmutableBitSet key : keys) {
          if (columns.contains(key)) {
            return true;
          }
        }
        return false;
      }

      public List<RelCollation> getCollations() {
        return collations;
      }

      public RelDistribution getDistribution() {
        return RelDistributionTraitDef.INSTANCE.getDefault();
      }
    };
  }
}

// End Statistics.java