/*
* 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.command.dml;
import java.util.ArrayList;
import java.util.HashSet;
import org.h2.api.ErrorCode;
import org.h2.command.Prepared;
import org.h2.engine.Database;
import org.h2.engine.Session;
import org.h2.expression.Alias;
import org.h2.expression.Expression;
import org.h2.expression.ExpressionColumn;
import org.h2.expression.ExpressionVisitor;
import org.h2.expression.Parameter;
import org.h2.expression.ValueExpression;
import org.h2.message.DbException;
import org.h2.result.LocalResult;
import org.h2.result.ResultTarget;
import org.h2.result.SortOrder;
import org.h2.table.ColumnResolver;
import org.h2.table.Table;
import org.h2.table.TableFilter;
import org.h2.util.New;
import org.h2.value.Value;
import org.h2.value.ValueInt;
import org.h2.value.ValueNull;
/**
* Represents a SELECT statement (simple, or union).
*/
//调用顺序 init=>prepare->query
public abstract class Query extends Prepared {
/**
* The limit expression as specified in the LIMIT or TOP clause.
*/
protected Expression limitExpr;
/**
* The offset expression as specified in the LIMIT .. OFFSET clause.
*/
protected Expression offsetExpr;
/**
* The sample size expression as specified in the SAMPLE_SIZE clause.
*/
protected Expression sampleSizeExpr;
/**
* Whether the result must only contain distinct rows.
*/
protected boolean distinct;
/**
* Whether the result needs to support random access.
*/
protected boolean randomAccessResult; //在ConditionInSelect时会设为true
private boolean noCache;
private int lastLimit;
private long lastEvaluated;
private LocalResult lastResult;
private Value[] lastParameters;
private boolean cacheableChecked;
Query(Session session) {
super(session);
}
/**
* Check if this is a UNION query.
*
* @return {@code true} if this is a UNION query
*/
public abstract boolean isUnion();
/**
* Prepare join batching.
*/
public abstract void prepareJoinBatch();
/**
* Execute the query without checking the cache. If a target is specified,
* the results are written to it, and the method returns null. If no target
* is specified, a new LocalResult is created and returned.
*
* @param limit the limit as specified in the JDBC method call
* @param target the target to write results to
* @return the result
*/
protected abstract LocalResult queryWithoutCache(int limit,
ResultTarget target);
/**
* Initialize the query.
*/
public abstract void init();
/**
* The the list of select expressions.
* This may include invisible expressions such as order by expressions.
*
* @return the list of expressions
*/
public abstract ArrayList<Expression> getExpressions();
/**
* Calculate the cost to execute this query.
*
* @return the cost
*/
public abstract double getCost();
/**
* Calculate the cost when used as a subquery.
* This method returns a value between 10 and 1000000,
* to ensure adding other values can't result in an integer overflow.
*
* @return the estimated cost as an integer
*/
public int getCostAsExpression() {
// ensure the cost is not larger than 1 million,
// so that adding other values can't overflow
return (int) Math.min(1000000.0, 10.0 + 10.0 * getCost());
}
/**
* Get all tables that are involved in this query.
*
* @return the set of tables
*/
public abstract HashSet<Table> getTables();
/**
* Set the order by list.
*
* @param order the order by list
*/
public abstract void setOrder(ArrayList<SelectOrderBy> order);
/**
* Whether the query has an order.
*
* @return true if it has
*/
public abstract boolean hasOrder();
/**
* Set the 'for update' flag.
*
* @param forUpdate the new setting
*/
public abstract void setForUpdate(boolean forUpdate);
/**
* Get the column count of this query.
*
* @return the column count
*/
public abstract int getColumnCount();
/**
* Map the columns to the given column resolver.
*
* @param resolver
* the resolver
* @param level
* the subquery level (0 is the top level query, 1 is the first
* subquery level)
*/
public abstract void mapColumns(ColumnResolver resolver, int level);
/**
* Change the evaluatable flag. This is used when building the execution
* plan.
*
* @param tableFilter the table filter
* @param b the new value
*/
public abstract void setEvaluatable(TableFilter tableFilter, boolean b);
/**
* Add a condition to the query. This is used for views.
*
* @param param the parameter
* @param columnId the column index (0 meaning the first column)
* @param comparisonType the comparison type
*/
public abstract void addGlobalCondition(Parameter param, int columnId, int comparisonType); //在ViewIndex中有使用
/**
* Check whether adding condition to the query is allowed. This is not
* allowed for views that have an order by and a limit, as it would affect
* the returned results.
*
* @return true if adding global conditions is allowed
*/
public abstract boolean allowGlobalConditions(); //在ViewIndex中有使用
/**
* Check if this expression and all sub-expressions can fulfill a criteria.
* If any part returns false, the result is false.
*
* @param visitor the visitor
* @return if the criteria can be fulfilled
*/
public abstract boolean isEverything(ExpressionVisitor visitor);
/**
* Update all aggregate function values.
*
* @param s the session
*/
public abstract void updateAggregate(Session s);
/**
* Call the before triggers on all tables.
*/
public abstract void fireBeforeSelectTriggers();
/**
* Set the distinct flag.
*
* @param b the new value
*/
public void setDistinct(boolean b) {
distinct = b;
}
public boolean isDistinct() {
return distinct;
}
/**
* Whether results need to support random access.
*
* @param b the new value
*/
public void setRandomAccessResult(boolean b) { //在ConditionInSelect时会设为true
randomAccessResult = b;
}
@Override
public boolean isQuery() {
return true;
}
@Override
public boolean isTransactional() {
return true;
}
/**
* Disable caching of result sets.
*/
public void disableCache() { //在ViewIndex中有使用
this.noCache = true;
}
private boolean sameResultAsLast(Session s, Value[] params,
Value[] lastParams, long lastEval) {
if (!cacheableChecked) {
long max = getMaxDataModificationId();
noCache = max == Long.MAX_VALUE;
cacheableChecked = true;
}
if (noCache) {
return false;
}
Database db = s.getDatabase();
for (int i = 0; i < params.length; i++) { //检查当前参数与上一次的参数是否相等
Value a = lastParams[i], b = params[i];
if (a.getType() != b.getType() || !db.areEqual(a, b)) {
return false;
}
}
if (!isEverything(ExpressionVisitor.DETERMINISTIC_VISITOR) ||
!isEverything(ExpressionVisitor.INDEPENDENT_VISITOR)) {
return false;
}
//数据有变时不使用缓存
if (db.getModificationDataId() > lastEval && getMaxDataModificationId() > lastEval) {
return false;
}
return true;
}
public final Value[] getParameterValues() {
ArrayList<Parameter> list = getParameters();
if (list == null) {
list = New.arrayList();
}
int size = list.size();
Value[] params = new Value[size];
for (int i = 0; i < size; i++) {
Value v = list.get(i).getParamValue();
params[i] = v;
}
return params;
}
@Override
public LocalResult query(int maxrows) {
return query(maxrows, null);
}
/**
* Execute the query, writing the result to the target result.
*
* @param limit the maximum number of rows to return
* @param target the target result (null will return the result)
* @return the result set (if the target is not set).
*/
LocalResult query(int limit, ResultTarget target) { //子类SelectUnion覆盖了此方法
fireBeforeSelectTriggers();
if (noCache || !session.getDatabase().getOptimizeReuseResults()) { //不使用缓存
return queryWithoutCache(limit, target);
}
Value[] params = getParameterValues();
long now = session.getDatabase().getModificationDataId();
if (isEverything(ExpressionVisitor.DETERMINISTIC_VISITOR)) {
if (lastResult != null && !lastResult.isClosed() &&
limit == lastLimit) {
if (sameResultAsLast(session, params, lastParameters,
lastEvaluated)) {
lastResult = lastResult.createShallowCopy(session);
if (lastResult != null) {
lastResult.reset();
return lastResult;
}
}
}
}
lastParameters = params;
closeLastResult();
LocalResult r = queryWithoutCache(limit, target);
lastResult = r;
this.lastEvaluated = now;
lastLimit = limit;
return r;
}
private void closeLastResult() {
if (lastResult != null) {
lastResult.close();
}
}
/**
* Initialize the order by list. This call may extend the expressions list.
*
* @param session the session
* @param expressions the select list expressions
* @param expressionSQL the select list SQL snippets
* @param orderList the order by list
* @param visible the number of visible columns in the select list
* @param mustBeInResult all order by expressions must be in the select list
* @param filters the table filters
*/
static void initOrder(Session session,
ArrayList<Expression> expressions,
ArrayList<String> expressionSQL,
ArrayList<SelectOrderBy> orderList,
int visible,
boolean mustBeInResult,
ArrayList<TableFilter> filters) {
Database db = session.getDatabase();
for (SelectOrderBy o : orderList) {
//类似这样的sql时:select name,id from mytable order by 1 desc
//o.expression为null，“order by 1”表示使用select字段列表中的第一个(就是name)来排序
//此时o.columnIndexExpr是1
Expression e = o.expression;
if (e == null) {
continue;
}
// special case: SELECT 1 AS A FROM DUAL ORDER BY A
// (oracle supports it, but only in order by, not in group by and
// not in having):
// SELECT 1 AS A FROM DUAL ORDER BY -A
boolean isAlias = false;
int idx = expressions.size(); //排序列最后放在什么位置，默认是最后，除非在select字段列表中找到了
if (e instanceof ExpressionColumn) {
// order by expression
ExpressionColumn exprCol = (ExpressionColumn) e;
String tableAlias = exprCol.getOriginalTableAliasName();
String col = exprCol.getOriginalColumnName();
for (int j = 0; j < visible; j++) {
boolean found = false;
Expression ec = expressions.get(j);
if (ec instanceof ExpressionColumn) {
// select expression
ExpressionColumn c = (ExpressionColumn) ec;
found = db.equalsIdentifiers(col, c.getColumnName());
if (found && tableAlias != null) {
String ca = c.getOriginalTableAliasName();
if (ca == null) {
found = false;
if (filters != null) {
// select id from test order by test.id
for (int i = 0, size = filters.size(); i < size; i++) {
TableFilter f = filters.get(i);
if (db.equalsIdentifiers(f.getTableAlias(), tableAlias)) {
found = true;
break;
}
}
}
} else {
found = db.equalsIdentifiers(ca, tableAlias);
}
}
} else if (!(ec instanceof Alias)) {
continue;
} else if (tableAlias == null && db.equalsIdentifiers(col, ec.getAlias())) {
found = true;
} else {
Expression ec2 = ec.getNonAliasExpression();
if (ec2 instanceof ExpressionColumn) {
ExpressionColumn c2 = (ExpressionColumn) ec2;
String ta = exprCol.getSQL();
String tb = c2.getSQL();
String s2 = c2.getColumnName();
found = db.equalsIdentifiers(col, s2);
if (!db.equalsIdentifiers(ta, tb)) {
found = false;
}
}
}
if (found) {
idx = j;
isAlias = true;
break;
}
}
} else {
String s = e.getSQL();
if (expressionSQL != null) {
for (int j = 0, size = expressionSQL.size(); j < size; j++) {
String s2 = expressionSQL.get(j);
if (db.equalsIdentifiers(s2, s)) {
idx = j;
isAlias = true;
break;
}
}
}
}
//在select中加distinct时distinct变量为true
//此时如果order by子句中的字段在select字段列表中不存在，那么就认为是错误
//比如select distinct name from mytable order by id desc是错的
//错误提示: org.h2.jdbc.JdbcSQLException: Order by expression "ID" must be in the result list in this case;
//这样就没问题select name from mytable order by id desc
//会自动加order by中的字段到select字段列表中
if (!isAlias) {
if (mustBeInResult) {
throw DbException.get(ErrorCode.ORDER_BY_NOT_IN_RESULT,
e.getSQL());
}
expressions.add(e);
String sql = e.getSQL();
expressionSQL.add(sql);
}
o.columnIndexExpr = ValueExpression.get(ValueInt.get(idx + 1));
Expression expr = expressions.get(idx).getNonAliasExpression();
o.expression = expr;
}
}
/**
* Create a {@link SortOrder} object given the list of {@link SelectOrderBy}
* objects. The expression list is extended if necessary.
*
* @param orderList a list of {@link SelectOrderBy} elements
* @param expressionCount the number of columns in the query
* @return the {@link SortOrder} object
*/
//order by字段列表在select字段列表中的位置索引(从0开始计数)和order by字段排序类型生成两个数组:indexes、sortTypes
//得到一个综合的SortOrder实例
public SortOrder prepareOrder(ArrayList<SelectOrderBy> orderList, int expressionCount) {
int size = orderList.size();
int[] index = new int[size];
int[] sortType = new int[size];
for (int i = 0; i < size; i++) {
SelectOrderBy o = orderList.get(i);
int idx;
boolean reverse = false;
Expression expr = o.columnIndexExpr;
Value v = expr.getValue(null);
if (v == ValueNull.INSTANCE) {
// parameter not yet set - order by first column
idx = 0;
} else {
idx = v.getInt();
if (idx < 0) {
reverse = true;
idx = -idx;
}
idx -= 1;
if (idx < 0 || idx >= expressionCount) {
throw DbException.get(ErrorCode.ORDER_BY_NOT_IN_RESULT, "" + (idx + 1));
}
}
index[i] = idx;
boolean desc = o.descending;
if (reverse) {
desc = !desc;
}
int type = desc ? SortOrder.DESCENDING : SortOrder.ASCENDING;
if (o.nullsFirst) {
type += SortOrder.NULLS_FIRST;
} else if (o.nullsLast) {
type += SortOrder.NULLS_LAST;
}
sortType[i] = type;
}
return new SortOrder(session.getDatabase(), index, sortType, orderList);
}
public void setOffset(Expression offset) {
this.offsetExpr = offset;
}
public Expression getOffset() {
return offsetExpr;
}
public void setLimit(Expression limit) {
this.limitExpr = limit;
}
public Expression getLimit() {
return limitExpr;
}
/**
* Add a parameter to the parameter list.
*
* @param param the parameter to add
*/
void addParameter(Parameter param) {
if (parameters == null) {
parameters = New.arrayList();
}
parameters.add(param);
}
public void setSampleSize(Expression sampleSize) {
this.sampleSizeExpr = sampleSize;
}
/**
* Get the sample size, if set.
*
* @param session the session
* @return the sample size
*/
int getSampleSizeValue(Session session) {
if (sampleSizeExpr == null) {
return 0;
}
//在Parser中已经调用过一次optimize
Value v = sampleSizeExpr.optimize(session).getValue(session);
if (v == ValueNull.INSTANCE) {
return 0;
}
return v.getInt();
}
public final long getMaxDataModificationId() {
//获得SQL语句(包括表达式中)涉及到的表或Sequence的ModificationId的最大值
ExpressionVisitor visitor = ExpressionVisitor.getMaxModificationIdVisitor();
isEverything(visitor);
return visitor.getMaxDataModificationId();
}
}