Package edu.caltech.nanodb.plannodes

Class ProjectNode

java.lang.Object

edu.caltech.nanodb.plannodes.PlanNode

edu.caltech.nanodb.plannodes.ProjectNode

All Implemented Interfaces:

java.lang.Cloneable

public class ProjectNode
extends PlanNode

PlanNode representing the SELECT clause in a SQL query. This is the relational algebra Project operator.

Field Summary

Fields

Modifier and Type	Field	Description
private Tuple	currentTuple	Current tuple the node is projecting (in NON-projected form).
private boolean	done	True if we have finished pulling tuples from children.
private static int	GUESS_NUM_UNIQUE_VALUES	This is our guess of how many unique values will be produced by a project expression, when we cannot determine it from the child plan's statistics.
private PlanCost	inputCost	The cost of the input subplan.
private Schema	inputSchema	The schema of tuples produced by the subplan.
private static org.apache.logging.log4j.Logger	logger	A logging object for reporting anything interesting that happens.
private java.util.List<ColumnInfo>	nonWildcardColumnInfos	This collection holds the non-wildcard column information, so that we can more easily assign schema to projected tuples.
private java.util.List<SelectValue>	projectionSpec	The new schema that this project node creates
private boolean	projectIsTrivial	This flag is set to true if the project is a trivial projection, where tuples are passed through unmodified.

Fields inherited from class edu.caltech.nanodb.plannodes.PlanNode

cost, environment, leftChild, rightChild, schema, stats

Constructor Summary

Constructors

Constructor	Description
ProjectNode(PlanNode leftChild, java.util.List<SelectValue> projectionSpec)	Constructs a ProjectNode that pulls tuples from a child node.
ProjectNode(java.util.List<SelectValue> projectionSpec)	Constructs a "leaf ProjectNode"; i.e.

Method Summary

Modifier and Type	Method	Description
private void	advanceCurrentTuple()	Helper function that advances the current tuple reference in the node.
void	cleanUp()	Perform any necessary clean up tasks.
protected PlanNode	clone()	Creates a copy of this project node and its subtree.
boolean	equals(java.lang.Object obj)	Checks if the argument is a plan node tree with the same structure, but not necesarily the same references.
Tuple	getNextTuple()	Gets the next tuple and projects it.
int	hashCode()	Computes and returns the hash-code of a project node.
void	initialize()	Do initialization for the select operation.
boolean	isTrivial()	Returns true if the project node is a trivial * projection with no table references.
void	markCurrentPosition()	Marks the current tuple in the tuple-stream produced by this node.
void	prepare()	This method is responsible for computing critical details about the plan node, such as the schema of the results that are produced, the estimated cost of evaluating the plan node (and its children), and statistics describing the results produced by the plan node.
protected void	prepareSchemaStats(Schema inputSchema, java.util.ArrayList<ColumnStats> inputStats)	This helper function computes the schema of the project plan-node, based on the schema of its child-plan, and also the expressions specified in the project operation.
private Tuple	projectTuple(Tuple tuple)	This helper method takes an input tuple and projects it to a result tuple based on the project
void	resetToLastMark()	Resets the node's tuple-stream to the most recently marked position.
java.util.List<OrderByExpression>	resultsOrderedBy()	Determines whether the results of the node are sorted.
boolean	supportsMarking()	This node supports marking if its subplan supports marking.
java.lang.String	toString()	Returns a string representing this project node's details.
private void	updateTrivialFlag()	This helper method sets the projectIsTrivial flag based on whether the passed-in projection specification is a single wildcard operation that would allow tuples to pass through unmodified.

Methods inherited from class edu.caltech.nanodb.plannodes.PlanNode

addParentEnvironmentToPlanTree, duplicate, getCost, getEnvironment, getSchema, getStats, printNodeTree, printNodeTree, printNodeTree, printNodeTreeToString, printNodeTreeToString, requiresLeftMarking, requiresRightMarking, setEnvironment

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

logger

private static org.apache.logging.log4j.Logger logger

A logging object for reporting anything interesting that happens.

GUESS_NUM_UNIQUE_VALUES

private static final int GUESS_NUM_UNIQUE_VALUES

This is our guess of how many unique values will be produced by a project expression, when we cannot determine it from the child plan's statistics.

See Also:

Constant Field Values

inputSchema

private Schema inputSchema

The schema of tuples produced by the subplan.

inputCost

private PlanCost inputCost

The cost of the input subplan.

projectionSpec

private java.util.List<SelectValue> projectionSpec

The new schema that this project node creates

projectIsTrivial

private boolean projectIsTrivial

This flag is set to true if the project is a trivial projection, where tuples are passed through unmodified.

nonWildcardColumnInfos

private java.util.List<ColumnInfo> nonWildcardColumnInfos

This collection holds the non-wildcard column information, so that we can more easily assign schema to projected tuples.

currentTuple

private Tuple currentTuple

Current tuple the node is projecting (in NON-projected form).

done

private boolean done

True if we have finished pulling tuples from children.

Constructor Detail

ProjectNode

public ProjectNode(PlanNode leftChild,
                   java.util.List<SelectValue> projectionSpec)

Constructs a ProjectNode that pulls tuples from a child node.

Parameters:

leftChild - the child to pull tuples from

projectionSpec - the set of expressions specifying how to project input tuples.

ProjectNode

public ProjectNode(java.util.List<SelectValue> projectionSpec)

Constructs a "leaf ProjectNode"; i.e. one that doesn't pull tuples from anywhere, but rather generates one tuple from its projection specification and then stops.

Parameters:

projectionSpec - the set of expressions specifying how to project input tuples.

Method Detail

updateTrivialFlag

private void updateTrivialFlag()

This helper method sets the projectIsTrivial flag based on whether the passed-in projection specification is a single wildcard operation that would allow tuples to pass through unmodified.

isTrivial

public boolean isTrivial()

Returns true if the project node is a trivial * projection with no table references. If the projection is trivial then it could even be removed.

Returns:

true if the select value is a full wildcard value, not even specifying a table name

prepare

public void prepare()

Description copied from class: PlanNode

This method is responsible for computing critical details about the plan node, such as the schema of the results that are produced, the estimated cost of evaluating the plan node (and its children), and statistics describing the results produced by the plan node.

Specified by:

prepare in class PlanNode

prepareSchemaStats

protected void prepareSchemaStats(Schema inputSchema,
                                  java.util.ArrayList<ColumnStats> inputStats)

This helper function computes the schema of the project plan-node, based on the schema of its child-plan, and also the expressions specified in the project operation.

resultsOrderedBy

public java.util.List<OrderByExpression> resultsOrderedBy()

Determines whether the results of the node are sorted.

Specified by:

resultsOrderedBy in class PlanNode

Returns:

If the plan node produces ordered results, this will be a list of objects specifying the ordering. If the node doesn't produce ordered results then the return-value will either be an empty list or it will be null.

supportsMarking

public boolean supportsMarking()

This node supports marking if its subplan supports marking.

Overrides:

supportsMarking in class PlanNode

Returns:

true if the node supports position marking, false otherwise.

getNextTuple

public Tuple getNextTuple()

Gets the next tuple and projects it.

Specified by:

getNextTuple in class PlanNode

Returns:

the tuple to be passed up to the next node.

advanceCurrentTuple

private void advanceCurrentTuple()

Helper function that advances the current tuple reference in the node.

projectTuple

private Tuple projectTuple(Tuple tuple)

This helper method takes an input tuple and projects it to a result tuple based on the project

Parameters:

tuple - the tuple to project

Returns:

the projected version of the tuple

initialize

public void initialize()

Do initialization for the select operation. Resets state variables.

Overrides:

initialize in class PlanNode

markCurrentPosition

public void markCurrentPosition()

Description copied from class: PlanNode

Marks the current tuple in the tuple-stream produced by this node. The PlanNode.resetToLastMark() method can be used to return to this tuple. Note that only one marker can be set in the tuple-stream at a time.

Overrides:

markCurrentPosition in class PlanNode

resetToLastMark

public void resetToLastMark()

Description copied from class: PlanNode

Resets the node's tuple-stream to the most recently marked position. Note that only one marker can be set in the tuple-stream at a time.

Overrides:

resetToLastMark in class PlanNode

cleanUp

public void cleanUp()

Description copied from class: PlanNode

Perform any necessary clean up tasks. This should probably be called when we are done with this plan node.

Specified by:

cleanUp in class PlanNode

equals

public boolean equals(java.lang.Object obj)

Checks if the argument is a plan node tree with the same structure, but not necesarily the same references.

Specified by:

equals in class PlanNode

Parameters:

obj - the object to which we are comparing

hashCode

public int hashCode()

Computes and returns the hash-code of a project node.

Specified by:

hashCode in class PlanNode

Returns:

the hash code for the plan node and any subnodes it may contain.

toString

public java.lang.String toString()

Returns a string representing this project node's details.

Specified by:

toString in class PlanNode

Returns:

a string representing this project-node.

clone

protected PlanNode clone()
                  throws java.lang.CloneNotSupportedException

Creates a copy of this project node and its subtree. This method is used by PlanNode.duplicate() to copy a plan tree.

Overrides:

clone in class PlanNode

Throws:

java.lang.CloneNotSupportedException