/*
* Copyright 2004-2014 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.result;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import org.h2.command.dml.SelectOrderBy;
import org.h2.engine.Database;
import org.h2.engine.SysProperties;
import org.h2.expression.Expression;
import org.h2.expression.ExpressionColumn;
import org.h2.table.Column;
import org.h2.table.TableFilter;
import org.h2.util.StatementBuilder;
import org.h2.util.StringUtils;
import org.h2.util.Utils;
import org.h2.value.Value;
import org.h2.value.ValueNull;
/**
* A sort order represents an ORDER BY clause in a query.
*/
public class SortOrder implements Comparator<Value[]> {
/**
* This bit mask means the values should be sorted in ascending order.
*/
public static final int ASCENDING = 0;
/**
* This bit mask means the values should be sorted in descending order.
*/
public static final int DESCENDING = 1;
/**
* This bit mask means NULLs should be sorted before other data, no matter
* if ascending or descending order is used.
*/
public static final int NULLS_FIRST = 2;
/**
* This bit mask means NULLs should be sorted after other data, no matter
* if ascending or descending order is used.
*/
public static final int NULLS_LAST = 4;
/**
* The default sort order for NULL.
*/
private static final int DEFAULT_NULL_SORT =
SysProperties.SORT_NULLS_HIGH ? 1 : -1;
private final Database database;
/**
* The column indexes of the order by expressions within the query.
*/
private final int[] queryColumnIndexes;
/**
* The sort type bit mask (DESCENDING, NULLS_FIRST, NULLS_LAST).
*/
private final int[] sortTypes;
/**
* The order list.
*/
private final ArrayList<SelectOrderBy> orderList;
/**
* Construct a new sort order object.
*
* @param database the database
* @param queryColumnIndexes the column index list
* @param sortType the sort order bit masks
* @param orderList the original query order list (if this is a query)
*/
public SortOrder(Database database, int[] queryColumnIndexes,
int[] sortType, ArrayList<SelectOrderBy> orderList) {
this.database = database;
this.queryColumnIndexes = queryColumnIndexes;
this.sortTypes = sortType;
this.orderList = orderList;
}
/**
* Create the SQL snippet that describes this sort order.
* This is the SQL snippet that usually appears after the ORDER BY clause.
*
* @param list the expression list
* @param visible the number of columns in the select list
* @return the SQL snippet
*/
public String getSQL(Expression[] list, int visible) {
StatementBuilder buff = new StatementBuilder();
int i = 0;
for (int idx : queryColumnIndexes) {
buff.appendExceptFirst(", ");
if (idx < visible) {
buff.append(idx + 1);
} else {
buff.append('=').append(StringUtils.unEnclose(list[idx].getSQL()));
}
int type = sortTypes[i++];
if ((type & DESCENDING) != 0) {
buff.append(" DESC");
}
if ((type & NULLS_FIRST) != 0) {
buff.append(" NULLS FIRST");
} else if ((type & NULLS_LAST) != 0) {
buff.append(" NULLS LAST");
}
}
return buff.toString();
}
/**
* Compare two expressions where one of them is NULL.
*
* @param aNull whether the first expression is null
* @param sortType the sort bit mask to use
* @return the result of the comparison (-1 meaning the first expression
* should appear before the second, 0 if they are equal)
*/
public static int compareNull(boolean aNull, int sortType) {
if ((sortType & NULLS_FIRST) != 0) {
return aNull ? -1 : 1;
} else if ((sortType & NULLS_LAST) != 0) {
return aNull ? 1 : -1;
} else {
// see also JdbcDatabaseMetaData.nullsAreSorted*
int comp = aNull ? DEFAULT_NULL_SORT : -DEFAULT_NULL_SORT;
return (sortType & DESCENDING) == 0 ? comp : -comp;
}
}
/**
* Compare two expression lists.
*
* @param a the first expression list
* @param b the second expression list
* @return the result of the comparison
*/
@Override
public int compare(Value[] a, Value[] b) {
for (int i = 0, len = queryColumnIndexes.length; i < len; i++) {
int idx = queryColumnIndexes[i];
int type = sortTypes[i];
Value ao = a[idx];
Value bo = b[idx];
boolean aNull = ao == ValueNull.INSTANCE, bNull = bo == ValueNull.INSTANCE;
if (aNull || bNull) {
if (aNull == bNull) {
continue;
}
return compareNull(aNull, type);
}
int comp = database.compare(ao, bo);
if (comp != 0) {
return (type & DESCENDING) == 0 ? comp : -comp;
}
}
return 0;
}
/**
* Sort a list of rows.
*
* @param rows the list of rows
*/
public void sort(ArrayList<Value[]> rows) {
Collections.sort(rows, this);
}
/**
* Sort a list of rows using offset and limit.
*
* @param rows the list of rows
* @param offset the offset
* @param limit the limit
*/
public void sort(ArrayList<Value[]> rows, int offset, int limit) {
int rowsSize = rows.size();
if (rows.isEmpty() || offset >= rowsSize || limit == 0) {
return;
}
if (offset < 0) {
offset = 0;
}
if (offset + limit > rowsSize) {
limit = rowsSize - offset;
}
if (limit == 1 && offset == 0) {
rows.set(0, Collections.min(rows, this));
return;
}
Value[][] arr = rows.toArray(new Value[rowsSize][]);
Utils.sortTopN(arr, offset, limit, this);
for (int i = 0, end = Math.min(offset + limit, rowsSize); i < end; i++) {
rows.set(i, arr[i]);
}
}
/**
* Get the column index list. This is the column indexes of the order by
* expressions within the query.
* <p>
* For the query "select name, id from test order by id, name" this is {1,
* 0} as the first order by expression (the column "id") is the second
* column of the query, and the second order by expression ("name") is the
* first column of the query.
*
* @return the list
*/
public int[] getQueryColumnIndexes() {
return queryColumnIndexes;
}
/**
* Get the column for the given table filter, if the sort column is for this
* filter.
*
* @param index the column index (0, 1,..)
* @param filter the table filter
* @return the column, or null
*/
public Column getColumn(int index, TableFilter filter) {
if (orderList == null) {
return null;
}
SelectOrderBy order = orderList.get(index);
Expression expr = order.expression;
if (expr == null) {
return null;
}
expr = expr.getNonAliasExpression();
if (expr.isConstant()) {
return null;
}
if (!(expr instanceof ExpressionColumn)) {
return null;
}
ExpressionColumn exprCol = (ExpressionColumn) expr;
if (exprCol.getTableFilter() != filter) {
return null;
}
return exprCol.getColumn();
}
/**
* Get the sort order bit masks.
*
* @return the list
*/
public int[] getSortTypes() {
return sortTypes;
}
}