/*
* 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.index;
import java.util.ArrayList;
import java.util.HashSet;
import org.h2.engine.Session;
import org.h2.expression.Comparison;
import org.h2.message.DbException;
import org.h2.result.ResultInterface;
import org.h2.result.Row;
import org.h2.result.SearchRow;
import org.h2.result.SortOrder;
import org.h2.table.Column;
import org.h2.table.IndexColumn;
import org.h2.table.Table;
import org.h2.table.TableFilter;
import org.h2.value.Value;
import org.h2.value.ValueGeometry;
import org.h2.value.ValueNull;
/**
* The filter used to walk through an index. This class supports IN(..)
* and IN(SELECT ...) optimizations.
*
* @author Thomas Mueller
* @author Noel Grandin
* @author Nicolas Fortin, Atelier SIG, IRSTV FR CNRS 24888
*/
//根据where条件中的值来判断index从哪里开始找从哪里结束，
//比如where id>10 and id<20，就意味着要找(10，20)这个区间内的记录。
public class IndexCursor implements Cursor {
private Session session;
private final TableFilter tableFilter;
private Index index;
private Table table;
private IndexColumn[] indexColumns;
private boolean alwaysFalse;
private SearchRow start, end, intersects;
private Cursor cursor;
private Column inColumn;
private int inListIndex;
private Value[] inList;
private ResultInterface inResult;
private HashSet<Value> inResultTested;
public IndexCursor(TableFilter filter) {
this.tableFilter = filter;
}
public void setIndex(Index index) {
this.index = index;
this.table = index.getTable();
Column[] columns = table.getColumns();
//把表中的所有字段做一下标记，如果是索引字段，那么对应indexColumns数组中的元素不为null
indexColumns = new IndexColumn[columns.length];
IndexColumn[] idxCols = index.getIndexColumns();
if (idxCols != null) {
for (int i = 0, len = columns.length; i < len; i++) {
int idx = index.getColumnIndex(columns[i]);
if (idx >= 0) {
indexColumns[i] = idxCols[idx];
}
}
}
}
/**
* Prepare this index cursor to make a lookup in index.
*
* @param s Session.
* @param indexConditions Index conditions.
*/
public void prepare(Session s, ArrayList<IndexCondition> indexConditions) {
this.session = s;
alwaysFalse = false;
start = end = null;
inList = null;
inColumn = null;
inResult = null;
inResultTested = null;
intersects = null;
// don't use enhanced for loop to avoid creating objects
for (int i = 0, size = indexConditions.size(); i < size; i++) {
IndexCondition condition = indexConditions.get(i);
if (condition.isAlwaysFalse()) { //如: "select * from IndexCursorTest where 2>3
alwaysFalse = true;
break;
}
Column column = condition.getColumn();
if (condition.getCompareType() == Comparison.IN_LIST) {
if (start == null && end == null) {
if (canUseIndexForIn(column)) {
this.inColumn = column;
inList = condition.getCurrentValueList(s);
inListIndex = 0;
}
}
} else if (condition.getCompareType() == Comparison.IN_QUERY) {
if (start == null && end == null) {
if (canUseIndexForIn(column)) {
this.inColumn = column;
inResult = condition.getCurrentResult();
}
}
} else {
Value v = condition.getCurrentValue(s);
boolean isStart = condition.isStart();
boolean isEnd = condition.isEnd();
boolean isIntersects = condition.isSpatialIntersects();
int columnId = column.getColumnId();
if (columnId >= 0) {
IndexColumn idxCol = indexColumns[columnId];
if (idxCol != null && (idxCol.sortType & SortOrder.DESCENDING) != 0) {
// if the index column is sorted the other way, we swap
// end and start NULLS_FIRST / NULLS_LAST is not a
// problem, as nulls never match anyway
boolean temp = isStart;
isStart = isEnd;
isEnd = temp;
}
}
if (isStart) {
start = getSearchRow(start, columnId, v, true);
}
if (isEnd) {
end = getSearchRow(end, columnId, v, false);
}
if (isIntersects) {
intersects = getSpatialSearchRow(intersects, columnId, v);
}
if (isStart || isEnd) {
// an X=? condition will produce less rows than
// an X IN(..) condition
inColumn = null;
inList = null;
inResult = null;
}
//当OPTIMIZE_IS_NULL设为false时，
//对于这样的SELECT rownum, * FROM JoinTest1 LEFT OUTER JOIN JoinTest2 ON name2=null
//还是会返回JoinTest1的所有记录，JoinTest2中的全为null
if (!session.getDatabase().getSettings().optimizeIsNull) {
if (isStart && isEnd) {
if (v == ValueNull.INSTANCE) {
// join on a column=NULL is always false
alwaysFalse = true;
}
}
}
}
}
}
/**
* Re-evaluate the start and end values of the index search for rows.
*
* @param s the session
* @param indexConditions the index conditions
*/
public void find(Session s, ArrayList<IndexCondition> indexConditions) {
prepare(s, indexConditions);
if (inColumn != null) {
return;
}
if (!alwaysFalse) {
if (intersects != null && index instanceof SpatialIndex) {
cursor = ((SpatialIndex) index).findByGeometry(tableFilter,
start, end, intersects);
} else {
cursor = index.find(tableFilter, start, end);
}
}
}
private boolean canUseIndexForIn(Column column) {
if (inColumn != null) {
// only one IN(..) condition can be used at the same time
return false;
}
// The first column of the index must match this column,
// or it must be a VIEW index (where the column is null).
// Multiple IN conditions with views are not supported, see
// IndexCondition.getMask.
IndexColumn[] cols = index.getIndexColumns();
if (cols == null) {
return true;
}
IndexColumn idxCol = cols[0];
//idxCol.column == column这个条件肯定是满足的，因为在根据where构造索引条件时，这个字段就是第一个索引字段
return idxCol == null || idxCol.column == column;
}
private SearchRow getSpatialSearchRow(SearchRow row, int columnId, Value v) {
if (row == null) {
row = table.getTemplateRow();
} else if (row.getValue(columnId) != null) {
// if an object needs to overlap with both a and b,
// then it needs to overlap with the the union of a and b
// (not the intersection)
ValueGeometry vg = (ValueGeometry) row.getValue(columnId).
convertTo(Value.GEOMETRY);
v = ((ValueGeometry) v.convertTo(Value.GEOMETRY)).
getEnvelopeUnion(vg);
}
if (columnId < 0) {
row.setKey(v.getLong());
} else {
row.setValue(columnId, v);
}
return row;
}
private SearchRow getSearchRow(SearchRow row, int columnId, Value v,
boolean max) {
if (row == null) {
row = table.getTemplateRow();
} else {
v = getMax(row.getValue(columnId), v, max);
}
if (columnId < 0) {
row.setKey(v.getLong());
} else {
row.setValue(columnId, v);
}
return row;
}
private Value getMax(Value a, Value b, boolean bigger) {
if (a == null) {
return b;
} else if (b == null) {
return a;
}
if (session.getDatabase().getSettings().optimizeIsNull) {
// IS NULL must be checked later
if (a == ValueNull.INSTANCE) {
return b;
} else if (b == ValueNull.INSTANCE) {
return a;
}
}
int comp = a.compareTo(b, table.getDatabase().getCompareMode());
if (comp == 0) {
return a;
}
if (a == ValueNull.INSTANCE || b == ValueNull.INSTANCE) {
if (session.getDatabase().getSettings().optimizeIsNull) {
// column IS NULL AND column <op> <not null> is always false
return null;
}
}
if (!bigger) {
//对于END的场景，比如假设a=10，b=20，所以a.compareTo(b)<0，即comp=-1，所以comp = -comp = 1
//对于f < 10 and f < 20的场景，显然只要f<10就够了，所以comp>0时还是返回a
comp = -comp;
}
return comp > 0 ? a : b;
}
/**
* Check if the result is empty for sure.
*
* @return true if it is
*/
public boolean isAlwaysFalse() {
return alwaysFalse;
}
/**
* Get start search row.
*
* @return search row
*/
public SearchRow getStart() {
return start;
}
/**
* Get end search row.
*
* @return search row
*/
public SearchRow getEnd() {
return end;
}
@Override
public Row get() {
if (cursor == null) {
return null;
}
return cursor.get();
}
@Override
public SearchRow getSearchRow() {
return cursor.getSearchRow();
}
@Override
public boolean next() {
while (true) {
if (cursor == null) {
nextCursor();
if (cursor == null) {
return false;
}
}
if (cursor.next()) {
return true;
}
cursor = null;
}
}
private void nextCursor() {
if (inList != null) {
while (inListIndex < inList.length) {
Value v = inList[inListIndex++];
if (v != ValueNull.INSTANCE) {
find(v);
break;
}
}
} else if (inResult != null) {
while (inResult.next()) {
Value v = inResult.currentRow()[0];
if (v != ValueNull.INSTANCE) {
v = inColumn.convert(v);
if (inResultTested == null) {
inResultTested = new HashSet<Value>();
}
if (inResultTested.add(v)) {
find(v);
break;
}
}
}
}
}
private void find(Value v) {
v = inColumn.convert(v);
int id = inColumn.getColumnId();
if (start == null) {
start = table.getTemplateRow();
}
start.setValue(id, v);
cursor = index.find(tableFilter, start, start);
}
@Override
public boolean previous() {
throw DbException.throwInternalError(toString());
}
}