org.apache.derby.impl.sql.compile

Class GroupByNode

java.lang.Object

org.apache.derby.impl.sql.compile.QueryTreeNode

org.apache.derby.impl.sql.compile.ResultSetNode

org.apache.derby.impl.sql.compile.FromTable

org.apache.derby.impl.sql.compile.SingleChildResultSetNode

org.apache.derby.impl.sql.compile.GroupByNode

All Implemented Interfaces:

Node, Optimizable, Visitable

public class GroupByNode
extends SingleChildResultSetNode

A GroupByNode represents a result set for a grouping operation on a select. Note that this includes a SELECT with aggregates and no grouping columns (in which case the select list is null) It has the same description as its input result set.

For the most part, it simply delegates operations to its bottomPRSet, which is currently expected to be a ProjectRestrictResultSet generated for a SelectNode.

NOTE: A GroupByNode extends FromTable since it can exist in a FromList.

There is a lot of room for optimizations here:

• agg(distinct x) group by x => agg(x) group by x (for min and max)
• min()/max() use index scans if possible, no sort may be needed.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
private static class	GroupByNode.ExpressionSorter Comparator class for GROUP BY expression substitution.

Field Summary

Fields

Modifier and Type	Field and Description
private boolean	addDistinctAggregate
private int	addDistinctAggregateColumnNum
private AggregatorInfoList	aggInfo Information that is used at execution time to process aggregates.
private java.util.List	aggregateVector The list of all aggregates in the query block that contains this group by.
(package private) GroupByList	groupingList The GROUP BY list
private ValueNode	havingClause
private SubqueryList	havingSubquerys
private boolean	isInSortedOrder
(package private) FromTable	parent The parent to the GroupByNode.
private boolean	singleInputRowOptimization

Fields inherited from class org.apache.derby.impl.sql.compile.SingleChildResultSetNode

childResult, hasTrulyTheBestAccessPath

Fields inherited from class org.apache.derby.impl.sql.compile.FromTable

ADD_PLAN, bestAccessPath, bestCostEstimate, bestSortAvoidancePath, correlationName, corrTableName, currentAccessPath, hashKeyColumns, initialCapacity, level, LOAD_PLAN, loadFactor, maxCapacity, origTableName, REMOVE_PLAN, tableNumber, tableProperties, trulyTheBestAccessPath, userSpecifiedJoinStrategy

Fields inherited from class org.apache.derby.impl.sql.compile.ResultSetNode

costEstimate, cursorTargetTable, finalCostEstimate, insertSource, optimizer, referencedTableMap, resultColumns, resultSetNumber, scratchCostEstimate, statementResultSet

Fields inherited from class org.apache.derby.impl.sql.compile.QueryTreeNode

AUTOINCREMENT_CREATE_MODIFY, AUTOINCREMENT_INC_INDEX, AUTOINCREMENT_IS_AUTOINCREMENT_INDEX, AUTOINCREMENT_START_INDEX

Constructor Summary

Constructors

Constructor and Description
GroupByNode()

Method Summary

Modifier and Type	Method and Description
private void	addAggregateColumns() In the query rewrite involving aggregates, add the columns for aggregation.
private void	addAggregates() Add the extra result columns required by the aggregates to the result list.
private void	addDistinctAggregatesToOrderBy() Add any distinct aggregates to the order by list.
private void	addNewColumnsForAggregation() Add a whole slew of columns needed for aggregation.
private void	addNewPRNode() Add a new PR node for aggregation.
private java.util.ArrayList	addUnAggColumns() In the query rewrite for group by, add the columns on which we are doing the group by.
(package private) void	considerPostOptimizeOptimizations(boolean selectHasPredicates) Consider any optimizations after the optimizer has chosen a plan.
CostEstimate	estimateCost(OptimizablePredicateList predList, ConglomerateDescriptor cd, CostEstimate outerCost, Optimizer optimizer, RowOrdering rowOrdering) Estimate the cost of scanning this Optimizable using the given predicate list with the given conglomerate.
boolean	flattenableInFromSubquery(FromList fromList) Evaluate whether or not the subquery in a FromSubquery is flattenable.
void	generate(ActivationClassBuilder acb, MethodBuilder mb) generate the sort result set operating over the source resultset.
private void	genGroupedAggregateResultSet(ActivationClassBuilder acb, MethodBuilder mb) Generate the code to evaluate grouped aggregates.
private void	genScalarAggregateResultSet(ActivationClassBuilder acb, MethodBuilder mb) Generate the code to evaluate scalar aggregates.
private ResultColumn	getColumnReference(ResultColumn targetRC, DataDictionary dd) Method for creating a new result column referencing the one passed in.
(package private) boolean	getIsInSortedOrder() Get whether or not the source is in sorted order.
FromTable	getParent() Return the parent node to this one, if there is one.
void	init(java.lang.Object bottomPR, java.lang.Object groupingList, java.lang.Object aggregateVector, java.lang.Object havingClause, java.lang.Object havingSubquerys, java.lang.Object tableProperties, java.lang.Object nestingLevel) Intializer for a GroupByNode.
boolean	isOneRowResultSet() Return whether or not the underlying ResultSet tree will return a single row, at most.
(package private) ResultColumnDescriptor[]	makeResultDescriptors()
ResultSetNode	optimize(DataDictionary dataDictionary, PredicateList predicates, double outerRows) Optimize this GroupByNode.
CostEstimate	optimizeIt(Optimizer optimizer, OptimizablePredicateList predList, CostEstimate outerCost, RowOrdering rowOrdering) Choose the best access path for this Optimizable.
void	printSubNodes(int depth) Prints the sub-nodes of this object.
boolean	pushOptPredicate(OptimizablePredicate optimizablePredicate) Push an OptimizablePredicate down, if this node accepts it.
java.lang.String	toString() Convert this object to a String.

Methods inherited from class org.apache.derby.impl.sql.compile.SingleChildResultSetNode

acceptChildren, addNewPredicate, adjustForSortElimination, adjustForSortElimination, changeAccessPath, decrementLevel, ensurePredicateList, forUpdate, getChildResult, getFinalCostEstimate, getFromTableByName, getTrulyTheBestAccessPath, init, initAccessPaths, isNotExists, isOrderedOn, modifyAccessPaths, preprocess, pullOptPredicates, pushExpressions, referencesSessionSchema, referencesTarget, reflectionNeededForProjection, setChildResult, setLevel, subqueryReferencesTarget, updateBestPlanMap, updateTargetLockMode

Methods inherited from class org.apache.derby.impl.sql.compile.FromTable

assignCostEstimate, canBeOrdered, considerSortAvoidancePath, convertAbsoluteToRelativeColumnPosition, cursorTargetTable, feasibleJoinStrategy, fillInReferencedTableMap, flatten, getBaseTableName, getBestAccessPath, getBestSortAvoidancePath, getCorrelationName, getCostEstimate, getCurrentAccessPath, getExposedName, getLevel, getName, getNumColumnsReturned, getOrigTableName, getProperties, getResultColumnsForList, getSchemaDescriptor, getSchemaDescriptor, getScratchCostEstimate, getTableDescriptor, getTableName, getTableNumber, getUserSpecifiedJoinStrategy, hashKeyColumns, hasLargeObjectColumns, hasTableNumber, initialCapacity, isBaseTable, isCoveringIndex, isFlattenableJoinNode, isJoinColumnForRightOuterJoin, isMaterializable, isOneRowScan, isTargetTable, legalJoinOrder, loadFactor, LOJ_reorderable, markUpdatableByCursor, maxCapacity, memoryUsageOK, modifyAccessPath, needsSpecialRCLBinding, nextAccessPath, optimizeSubqueries, rememberAsBest, rememberJoinStrategyAsBest, rememberSortAvoidancePath, resetJoinStrategies, setCostEstimate, setHashKeyColumns, setOrigTableName, setProperties, setTableNumber, startOptimizing, supportsMultipleInstantiations, tellRowOrderingAboutConstantColumns, transformOuterJoins, uniqueJoin, verifyProperties

Methods inherited from class org.apache.derby.impl.sql.compile.ResultSetNode

assignResultSetNumber, bindExpressions, bindExpressionsWithTables, bindNonVTITables, bindResultColumns, bindResultColumns, bindTargetExpressions, bindUntypedNullsToResultColumns, bindVTITables, columnTypesAndLengthsMatch, considerMaterialization, enhanceRCLForInsert, generateNormalizationResultSet, generateResultSet, genProjectRestrict, genProjectRestrict, genProjectRestrictForReordering, getAllResultColumns, getCostEstimate, getCursorTargetTable, getFromList, getMatchingColumn, getNewCostEstimate, getOptimizer, getOptimizerImpl, getRCLForInsert, getReferencedTableMap, getResultColumns, getResultSetNumber, isPossibleDistinctScan, isUpdatableCursor, LOJgetReferencedTables, makeResultDescription, markAsCursorTargetTable, markForDistinctScan, markStatementResultSet, modifyAccessPaths, notCursorTargetTable, notFlattenableJoin, numDistinctAggregates, parseDefault, performMaterialization, projectResultColumns, pushOffsetFetchFirst, pushOrderByList, rejectParameters, rejectXMLValues, renameGeneratedResultNames, replaceOrForbidDefaults, returnsAtMostOneRow, setInsertSource, setReferencedTableMap, setResultColumns, setResultToBooleanTrueNode, setTableConstructorTypes, verifySelectStarSubquery

Methods inherited from class org.apache.derby.impl.sql.compile.QueryTreeNode

accept, bindOffsetFetch, bindRowMultiSet, bindUserCatalogType, bindUserType, checkReliability, checkReliability, convertDefaultNode, createTypeDependency, debugFlush, debugPrint, disablePrivilegeCollection, formatNodeString, foundString, generateAuthorizeCheck, getBeginOffset, getClassFactory, getCompilerContext, getContextManager, getCursorInfo, getDataDictionary, getDependencyManager, getEndOffset, getExecutionFactory, getGenericConstantActionFactory, getIntProperty, getLanguageConnectionContext, getNodeFactory, getNodeType, getNullNode, getParameterTypes, getSchemaDescriptor, getSchemaDescriptor, getStatementType, getTableDescriptor, getTypeCompiler, init, init, init, init, init, init, init, init, init, init, init, init, isAtomic, isInstanceOf, isPrivilegeCollectionRequired, isSessionSchema, isSessionSchema, makeConstantAction, makeTableName, makeTableName, nodeHeader, orReliability, parseStatement, printLabel, resolveTableToSynonym, setBeginOffset, setContextManager, setEndOffset, setNodeType, setRefActionInfo, stackPrint, treePrint, treePrint, verifyClassExist

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface org.apache.derby.iapi.sql.compile.Optimizable

getDataDictionary, getReferencedTableMap, getResultSetNumber

Field Detail

groupingList

GroupByList groupingList

The GROUP BY list

aggregateVector

private java.util.List aggregateVector

The list of all aggregates in the query block that contains this group by.

aggInfo

private AggregatorInfoList aggInfo

Information that is used at execution time to process aggregates.

parent

FromTable parent

The parent to the GroupByNode. If we need to generate a ProjectRestrict over the group by then this is set to that node. Otherwise it is null.

addDistinctAggregate

private boolean addDistinctAggregate

singleInputRowOptimization

private boolean singleInputRowOptimization

addDistinctAggregateColumnNum

private int addDistinctAggregateColumnNum

isInSortedOrder

private boolean isInSortedOrder

havingClause

private ValueNode havingClause

havingSubquerys

private SubqueryList havingSubquerys

Constructor Detail

GroupByNode

public GroupByNode()

Method Detail

init

public void init(java.lang.Object bottomPR,
                 java.lang.Object groupingList,
                 java.lang.Object aggregateVector,
                 java.lang.Object havingClause,
                 java.lang.Object havingSubquerys,
                 java.lang.Object tableProperties,
                 java.lang.Object nestingLevel)
          throws StandardException

Intializer for a GroupByNode.

Specified by:

init in interface Node

Overrides:

init in class QueryTreeNode

Parameters:

bottomPR - The child FromTable

groupingList - The groupingList

aggregateVector - The vector of aggregates from the query block. Since aggregation is done at the same time as grouping, we need them here.

havingClause - The having clause.

havingSubquerys - subqueries in the having clause.

tableProperties - Properties list associated with the table

nestingLevel - nestingLevel of this group by node. This is used for error checking of group by queries with having clause.

Throws:

StandardException - Thrown on error

getIsInSortedOrder

boolean getIsInSortedOrder()

Get whether or not the source is in sorted order.

Returns:

Whether or not the source is in sorted order.

addAggregates

private void addAggregates()
                    throws StandardException

Add the extra result columns required by the aggregates to the result list.

Throws:

standard - exception

StandardException

addDistinctAggregatesToOrderBy

private void addDistinctAggregatesToOrderBy()

Add any distinct aggregates to the order by list. Asserts that there are 0 or more distincts.

addNewPRNode

private void addNewPRNode()
                   throws StandardException

Add a new PR node for aggregation. Put the new PR under the sort.

Throws:

standard - exception

StandardException

addUnAggColumns

private java.util.ArrayList addUnAggColumns()
                                     throws StandardException

In the query rewrite for group by, add the columns on which we are doing the group by.

Returns:

havingRefsToSubstitute visitors array. Return any havingRefsToSubstitute visitors since it is too early to apply them yet; we need the AggregateNodes unmodified until after we add the new columns for aggregation (DERBY-4071).

Throws:

StandardException

See Also:

addNewColumnsForAggregation()

addNewColumnsForAggregation

private void addNewColumnsForAggregation()
                                  throws StandardException

Add a whole slew of columns needed for aggregation. Basically, for each aggregate we add 3 columns: the aggregate input expression and the aggregator column and a column where the aggregate result is stored. The input expression is taken directly from the aggregator node. The aggregator is the run time aggregator. We add it to the RC list as a new object coming into the sort node.

At this point this is invoked, we have the following tree:

PR - (PARENT): RCL is the original select list | PR - GROUP BY: RCL is empty | PR - FROM TABLE: RCL is empty

For each ColumnReference in PR RCL

• clone the ref
• create a new RC in the bottom RCL and set it to the col ref
• create a new RC in the GROUPBY RCL and set it to point to the bottom RC
• reset the top PR ref to point to the new GROUPBY RC

For each aggregate in aggregateVector

• create RC in FROM TABLE. Fill it with aggs Operator.
• create RC in FROM TABLE for agg result
• create RC in FROM TABLE for aggregator
• create RC in GROUPBY for agg input, set it to point to FROM TABLE RC
• create RC in GROUPBY for agg result
• create RC in GROUPBY for aggregator
• replace Agg with reference to RC for agg result

.

For a query like,

          select c1, sum(c2), max(c3)
          from t1 
          group by c1;
          

the query tree ends up looking like this:

            ProjectRestrictNode RCL -> (ptr to GBN(column[0]), ptr to GBN(column[1]), ptr to GBN(column[4]))
                      |
            GroupByNode RCL->(C1, SUM(C2), , , MAX(C3), , )
                      |
            ProjectRestrict RCL->(C1, C2, C3)
                      |
            FromBaseTable
            

The RCL of the GroupByNode contains all the unagg (or grouping columns) followed by 3 RC's for each aggregate in this order: the final computed aggregate value, the aggregate input and the aggregator function.

The Aggregator function puts the results in the first of the 3 RC's and the PR resultset in turn picks up the value from there.

The notation (ptr to GBN(column[0])) basically means that it is a pointer to the 0th RC in the RCL of the GroupByNode.

The addition of these unagg and agg columns to the GroupByNode and to the PRN is performed in addUnAggColumns and addAggregateColumns.

Note that that addition of the GroupByNode is done after the query is optimized (in SelectNode#modifyAccessPaths) which means a fair amount of patching up is needed to account for generated group by columns.

Throws:

standard - exception

StandardException

addAggregateColumns

private void addAggregateColumns()
                          throws StandardException

In the query rewrite involving aggregates, add the columns for aggregation.

Throws:

StandardException

See Also:

addNewColumnsForAggregation()

getParent

public FromTable getParent()

Return the parent node to this one, if there is one. It will return 'this' if there is no generated node above this one.

Returns:

the parent node

optimizeIt

public CostEstimate optimizeIt(Optimizer optimizer,
                               OptimizablePredicateList predList,
                               CostEstimate outerCost,
                               RowOrdering rowOrdering)
                        throws StandardException

Description copied from interface: Optimizable

Choose the best access path for this Optimizable.

Specified by:

optimizeIt in interface Optimizable

Overrides:

optimizeIt in class FromTable

Parameters:

optimizer - Optimizer to use.

predList - The predicate list to optimize against

outerCost - The CostEstimate for the outer tables in the join order, telling how many times this Optimizable will be scanned.

rowOrdering - The row ordering for all the tables in the join order, including this one.

Returns:

The optimizer's estimated cost of the best access path.

Throws:

StandardException - Thrown on error

See Also:

Optimizable.optimizeIt(org.apache.derby.iapi.sql.compile.Optimizer, org.apache.derby.iapi.sql.compile.OptimizablePredicateList, org.apache.derby.iapi.sql.compile.CostEstimate, org.apache.derby.iapi.sql.compile.RowOrdering)

estimateCost

public CostEstimate estimateCost(OptimizablePredicateList predList,
                                 ConglomerateDescriptor cd,
                                 CostEstimate outerCost,
                                 Optimizer optimizer,
                                 RowOrdering rowOrdering)
                          throws StandardException

Description copied from interface: Optimizable

Estimate the cost of scanning this Optimizable using the given predicate list with the given conglomerate. It is assumed that the predicate list has already been classified. This cost estimate is just for one scan, not for the life of the query.

Specified by:

estimateCost in interface Optimizable

Overrides:

estimateCost in class FromTable

Parameters:

predList - The predicate list to optimize against

cd - The conglomerate descriptor to get the cost of

outerCost - The estimated cost of the part of the plan outer to this optimizable.

optimizer - The optimizer to use to help estimate the cost

rowOrdering - The row ordering for all the tables in the join order, including this one.

Returns:

The estimated cost of doing the scan

Throws:

StandardException - Thrown on error

See Also:

Optimizable.estimateCost(org.apache.derby.iapi.sql.compile.OptimizablePredicateList, org.apache.derby.iapi.sql.dictionary.ConglomerateDescriptor, org.apache.derby.iapi.sql.compile.CostEstimate, org.apache.derby.iapi.sql.compile.Optimizer, org.apache.derby.iapi.sql.compile.RowOrdering)

pushOptPredicate

public boolean pushOptPredicate(OptimizablePredicate optimizablePredicate)
                         throws StandardException

Description copied from interface: Optimizable

Push an OptimizablePredicate down, if this node accepts it.

Specified by:

pushOptPredicate in interface Optimizable

Overrides:

pushOptPredicate in class FromTable

Parameters:

optimizablePredicate - OptimizablePredicate to push down.

Returns:

Whether or not the predicate was pushed down.

Throws:

StandardException - Thrown on error

See Also:

Optimizable.pushOptPredicate(org.apache.derby.iapi.sql.compile.OptimizablePredicate)

toString

public java.lang.String toString()

Convert this object to a String. See comments in QueryTreeNode.java for how this should be done for tree printing.

Overrides:

toString in class FromTable

Returns:

This object as a String

printSubNodes

public void printSubNodes(int depth)

Prints the sub-nodes of this object. See QueryTreeNode.java for how tree printing is supposed to work.

Overrides:

printSubNodes in class SingleChildResultSetNode

Parameters:

depth - The depth of this node in the tree

flattenableInFromSubquery

public boolean flattenableInFromSubquery(FromList fromList)

Evaluate whether or not the subquery in a FromSubquery is flattenable. Currently, a FSqry is flattenable if all of the following are true: o Subquery is a SelectNode. o It contains no top level subqueries. (RESOLVE - we can relax this) o It does not contain a group by or having clause o It does not contain aggregates.

Overrides:

flattenableInFromSubquery in class SingleChildResultSetNode

Parameters:

fromList - The outer from list

Returns:

boolean Whether or not the FromSubquery is flattenable.

optimize

public ResultSetNode optimize(DataDictionary dataDictionary,
                              PredicateList predicates,
                              double outerRows)
                       throws StandardException

Optimize this GroupByNode.

Overrides:

optimize in class SingleChildResultSetNode

Parameters:

dataDictionary - The DataDictionary to use for optimization

predicates - The PredicateList to optimize. This should be a join predicate.

outerRows - The number of outer joining rows

Returns:

ResultSetNode The top of the optimized subtree

Throws:

StandardException - Thrown on error

makeResultDescriptors

ResultColumnDescriptor[] makeResultDescriptors()

Overrides:

makeResultDescriptors in class ResultSetNode

isOneRowResultSet

public boolean isOneRowResultSet()
                          throws StandardException

Return whether or not the underlying ResultSet tree will return a single row, at most. This is important for join nodes where we can save the extra next on the right side if we know that it will return at most 1 row.

Overrides:

isOneRowResultSet in class SingleChildResultSetNode

Returns:

Whether or not the underlying ResultSet tree will return a single row.

Throws:

StandardException - Thrown on error

generate

public void generate(ActivationClassBuilder acb,
                     MethodBuilder mb)
              throws StandardException

generate the sort result set operating over the source resultset. Adds distinct aggregates to the sort if necessary.

Overrides:

generate in class QueryTreeNode

Parameters:

acb - The ActivationClassBuilder for the class being built

mb - The method for the generated code to go into

Throws:

StandardException - Thrown on error

genScalarAggregateResultSet

private void genScalarAggregateResultSet(ActivationClassBuilder acb,
                                         MethodBuilder mb)

Generate the code to evaluate scalar aggregates.

genGroupedAggregateResultSet

private void genGroupedAggregateResultSet(ActivationClassBuilder acb,
                                          MethodBuilder mb)
                                   throws StandardException

Generate the code to evaluate grouped aggregates.

Throws:

StandardException

getColumnReference

private ResultColumn getColumnReference(ResultColumn targetRC,
                                        DataDictionary dd)
                                 throws StandardException

Method for creating a new result column referencing the one passed in.

Parameters:

targetRC - the source

dd -

Returns:

the new result column

Throws:

StandardException - on error

considerPostOptimizeOptimizations

void considerPostOptimizeOptimizations(boolean selectHasPredicates)
                                throws StandardException

Consider any optimizations after the optimizer has chosen a plan. Optimizations include: o min optimization for scalar aggregates o max optimization for scalar aggregates

Parameters:

selectHasPredicates - true if SELECT containing this vector/scalar aggregate has a restriction

Throws:

StandardException - on error