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base on h2database 1.4.196. for more information, see http://h2database.com/
/*
* Copyright 2004-2018 H2 Group. Multiple-Licensed under the MPL 2.0,
* and the EPL 1.0 (http://h2database.com/html/license.html).
* Initial Developer: H2 Group
*/
package org.h2.expression;
import java.util.Arrays;
import java.util.Comparator;
import org.h2.engine.Constants;
import org.h2.engine.Database;
import org.h2.util.ValueHashMap;
import org.h2.value.CompareMode;
import org.h2.value.Value;
import org.h2.value.ValueArray;
import org.h2.value.ValueLong;
/**
* Data stored while calculating a HISTOGRAM aggregate.
*/
class AggregateDataHistogram extends AggregateData {
private long count;
private ValueHashMap distinctValues;
@Override
public void add(Database database, int dataType, boolean distinct, Value v) {
if (distinctValues == null) {
distinctValues = ValueHashMap.newInstance();
}
AggregateDataHistogram a = distinctValues.get(v);
if (a == null) {
if (distinctValues.size() < Constants.SELECTIVITY_DISTINCT_COUNT) {
a = new AggregateDataHistogram();
distinctValues.put(v, a);
}
}
if (a != null) {
a.count++;
}
}
@Override
public Value getValue(Database database, int dataType, boolean distinct) {
if (distinct) {
count = 0;
groupDistinct(database, dataType);
}
ValueArray[] values = new ValueArray[distinctValues.size()];
int i = 0;
for (Value dv : distinctValues.keys()) {
AggregateDataHistogram d = distinctValues.get(dv);
values[i] = ValueArray.get(new Value[] { dv, ValueLong.get(d.count) });
i++;
}
final CompareMode compareMode = database.getCompareMode();
Arrays.sort(values, new Comparator() {
@Override
public int compare(ValueArray v1, ValueArray v2) {
Value a1 = v1.getList()[0];
Value a2 = v2.getList()[0];
return a1.compareTo(a2, compareMode);
}
});
Value v = ValueArray.get(values);
return v.convertTo(dataType);
}
private void groupDistinct(Database database, int dataType) {
if (distinctValues == null) {
return;
}
count = 0;
for (Value v : distinctValues.keys()) {
add(database, dataType, false, v);
}
}
}