/*
* 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.expression;
import org.h2.api.ErrorCode;
import org.h2.command.dml.Query;
import org.h2.engine.Database;
import org.h2.engine.Session;
import org.h2.index.IndexCondition;
import org.h2.message.DbException;
import org.h2.result.LocalResult;
import org.h2.table.ColumnResolver;
import org.h2.table.TableFilter;
import org.h2.util.StringUtils;
import org.h2.value.Value;
import org.h2.value.ValueBoolean;
import org.h2.value.ValueNull;
/**
* An 'in' condition with a subquery, as in WHERE ID IN(SELECT ...)
*/
public class ConditionInSelect extends Condition {
private final Database database;
private Expression left;
private final Query query;
private final boolean all;
private final int compareType;
private int queryLevel; //没看到用处
public ConditionInSelect(Database database, Expression left, Query query,
boolean all, int compareType) {
this.database = database;
this.left = left;
this.query = query;
this.all = all;
this.compareType = compareType;
}
@Override
public Value getValue(Session session) {
query.setSession(session);
if (!query.hasOrder()) {
query.setDistinct(true);
}
LocalResult rows = query.query(0);
// 子查询没有记录时，如果是ALL类型的子查询，那么认为条件为true，
// 否则为false，
// 假设表中字段id的值是1到6，这条语句
// delete from ConditionInSelectTest where id > ALL(select id from ConditionInSelectTest where id>10)
// 里面的子查询没有值，所以where id<ALL()时都为true，实际上是删除所有记录
// 如果改成ANY，那么什么记录都不删
Value l = left.getValue(session);
if (rows.getRowCount() == 0) {
return ValueBoolean.get(all);
} else if (l == ValueNull.INSTANCE) { //如果left是null，那么返回null
return l;
}
if (!session.getDatabase().getSettings().optimizeInSelect) {
return getValueSlow(rows, l);
}
if (all || (compareType != Comparison.EQUAL &&
compareType != Comparison.EQUAL_NULL_SAFE)) {
return getValueSlow(rows, l);
}
//下面代码是处理非all，且是EQUAL或EQUAL_NULL_SAFE的情况
//获得结果集中第一列的类型
int dataType = rows.getColumnType(0);
//如果列的类型是null，那么返回false
if (dataType == Value.NULL) {
return ValueBoolean.get(false);
}
l = l.convertTo(dataType); //把left的值转成结果集中第一列的类型，然后判断结果集中是否包含它，返回true
if (rows.containsDistinct(new Value[] { l })) {
return ValueBoolean.get(true);
}
//结果集中不包含left且有null，那么返回null
if (rows.containsDistinct(new Value[] { ValueNull.INSTANCE })) {
return ValueNull.INSTANCE;
}
return ValueBoolean.get(false);
}
private Value getValueSlow(LocalResult rows, Value l) {
// this only returns the correct result if the result has at least one
// row, and if l is not null
boolean hasNull = false;
boolean result = all;
while (rows.next()) {
boolean value;
Value r = rows.currentRow()[0];
if (r == ValueNull.INSTANCE) {
value = false;
hasNull = true;
} else {
value = Comparison.compareNotNull(database, l, r, compareType);
}
if (!value && all) {
result = false;
break;
} else if (value && !all) {
result = true;
break;
}
}
if (!result && hasNull) {
return ValueNull.INSTANCE;
}
return ValueBoolean.get(result);
}
@Override
public void mapColumns(ColumnResolver resolver, int level) {
left.mapColumns(resolver, level);
query.mapColumns(resolver, level + 1);
this.queryLevel = Math.max(level, this.queryLevel); //没看到用处
}
@Override
public Expression optimize(Session session) {
left = left.optimize(session);
query.setRandomAccessResult(true);
//<<<<<<< HEAD
// query.prepare();
// //如where id in(select id,name from ConditionInSelectTest where id=3)
// //org.h2.jdbc.JdbcSQLException: Subquery is not a single column query
// //子查询不能多于1个列
//=======
session.optimizeQueryExpression(query);
if (query.getColumnCount() != 1) {
throw DbException.get(ErrorCode.SUBQUERY_IS_NOT_SINGLE_COLUMN);
}
// Can not optimize: the data may change
return this;
}
@Override
public void setEvaluatable(TableFilter tableFilter, boolean b) {
left.setEvaluatable(tableFilter, b);
query.setEvaluatable(tableFilter, b);
}
@Override
public String getSQL() {
StringBuilder buff = new StringBuilder();
buff.append('(').append(left.getSQL()).append(' ');
if (all) {
buff.append(Comparison.getCompareOperator(compareType)).
append(" ALL");
} else {
if (compareType == Comparison.EQUAL) {
buff.append("IN");
} else {
buff.append(Comparison.getCompareOperator(compareType)).
append(" ANY");
}
}
buff.append("(\n").append(StringUtils.indent(query.getPlanSQL(), 4, false)).
append("))");
return buff.toString();
}
@Override
public void updateAggregate(Session session) {
left.updateAggregate(session);
query.updateAggregate(session);
}
@Override
public boolean isEverything(ExpressionVisitor visitor) {
return left.isEverything(visitor) && query.isEverything(visitor);
}
@Override
public int getCost() {
return left.getCost() + query.getCostAsExpression();
}
@Override
public void createIndexConditions(Session session, TableFilter filter) {
if (!session.getDatabase().getSettings().optimizeInList) {
return;
}
if (!(left instanceof ExpressionColumn)) {
return;
}
ExpressionColumn l = (ExpressionColumn) left;
if (filter != l.getTableFilter()) {
return;
}
//query中的columnResolver与filter不是同一个实例时就把query加入索引条件
//也就是说如果query中的columnResolver与filter是同一个实例，
//就相当于filter自己找自己了，会出现死循环
ExpressionVisitor visitor = ExpressionVisitor.getNotFromResolverVisitor(filter);
if (!query.isEverything(visitor)) {
return;
}
filter.addIndexCondition(IndexCondition.getInQuery(l, query));
}
}