content: /*
   * 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.materialize;
  
  import org.apache.calcite.DataContexts;
  import org.apache.calcite.schema.ScannableTable;
  import org.apache.calcite.schema.Table;
  import org.apache.calcite.schema.impl.MaterializedViewTable;
  import org.apache.calcite.util.ImmutableBitSet;
  
  import com.google.common.collect.ImmutableList;
  import com.google.common.collect.Iterables;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.util.ArrayList;
  import java.util.List;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * Implementation of {@link LatticeStatisticProvider} that gets statistics by
   * executing "SELECT COUNT(DISTINCT ...) ..." SQL queries.
   */
  class SqlLatticeStatisticProvider implements LatticeStatisticProvider {
    static final Factory FACTORY = SqlLatticeStatisticProvider::new;
  
    static final Factory CACHED_FACTORY = lattice -> {
      LatticeStatisticProvider provider = FACTORY.apply(lattice);
      return new CachingLatticeStatisticProvider(lattice, provider);
    };
  
    private final Lattice lattice;
  
    /** Creates a SqlLatticeStatisticProvider. */
    private SqlLatticeStatisticProvider(Lattice lattice) {
      this.lattice = requireNonNull(lattice, "lattice");
    }
  
    @Override public double cardinality(List<Lattice.Column> columns) {
      final List<Double> counts = new ArrayList<>();
      for (Lattice.Column column : columns) {
        counts.add(cardinality(lattice, column));
      }
      return (int) Lattice.getRowCount(lattice.getFactRowCount(), counts);
    }
  
    private static double cardinality(Lattice lattice, Lattice.Column column) {
      final String sql = lattice.countSql(ImmutableBitSet.of(column.ordinal));
      final Table table =
          new MaterializationService.DefaultTableFactory()
              .createTable(lattice.rootSchema, sql, ImmutableList.of());
      final @Nullable Object[] values =
          Iterables.getOnlyElement(
              ((ScannableTable) table).scan(
                  DataContexts.of(MaterializedViewTable.MATERIALIZATION_CONNECTION,
                      lattice.rootSchema.plus())));
      Number value = (Number) values[0];
      requireNonNull(value, () -> "count(*) produced null in " + sql);
      return value.doubleValue();
    }
  }
  