org.h2.command.dml

Class Query

java.lang.Object

org.h2.command.Prepared

org.h2.command.dml.Query

Direct Known Subclasses:

Select, SelectUnion

public abstract class Query
extends Prepared

Represents a SELECT statement (simple, or union).

Field Summary

Fields

Modifier and Type	Field and Description
protected boolean	distinct Whether the result must only contain distinct rows.
protected Expression	limitExpr The limit expression as specified in the LIMIT or TOP clause.
protected Expression	offsetExpr The offset expression as specified in the LIMIT ..
protected boolean	randomAccessResult Whether the result needs to support random access.
protected int	sampleSize The sample size

Fields inherited from class org.h2.command.Prepared

create, parameters, prepareAlways, session, sqlStatement

Method Summary

Methods

Modifier and Type	Method and Description
abstract void	addGlobalCondition(Parameter param, int columnId, int comparisonType) Add a condition to the query.
void	disableCache() Disable caching of result sets.
abstract void	fireBeforeSelectTriggers() Call the before triggers on all tables.
abstract int	getColumnCount() Get the column count of this query.
abstract double	getCost() Calculate the cost to execute this query.
int	getCostAsExpression() Calculate the cost when used as a subquery.
abstract ArrayList<Expression>	getExpressions() The the list of select expressions.
long	getMaxDataModificationId()
Value[]	getParameterValues()
abstract HashSet<Table>	getTables() Get all tables that are involved in this query.
abstract void	init() Initialize the query.
abstract boolean	isEverything(ExpressionVisitor visitor) Check if this expression and all sub-expressions can fulfill a criteria.
boolean	isQuery() Check if this object is a query.
boolean	isTransactional() Check if this command is transactional.
abstract void	mapColumns(ColumnResolver resolver, int level) Map the columns to the given column resolver.
SortOrder	prepareOrder(ArrayList<SelectOrderBy> orderList, int expressionCount) Create a SortOrder object given the list of SelectOrderBy objects.
LocalResult	query(int maxrows) Execute the query.
protected abstract LocalResult	queryWithoutCache(int limit, ResultTarget target) Execute the query without checking the cache.
void	setDistinct(boolean b) Set the distinct flag.
abstract void	setEvaluatable(TableFilter tableFilter, boolean b) Change the evaluatable flag.
abstract void	setForUpdate(boolean forUpdate) Set the 'for update' flag.
void	setLimit(Expression limit)
void	setOffset(Expression offset)
abstract void	setOrder(ArrayList<SelectOrderBy> order) Set the order by list.
void	setRandomAccessResult(boolean b) Whether results need to support random access.
void	setSampleSize(int sampleSize)
abstract void	updateAggregate(Session s) Update all aggregate function values.

Methods inherited from class org.h2.command.Prepared

checkCanceled, checkParameters, getCurrentObjectId, getCurrentRowNumber, getObjectId, getParameters, getPlanSQL, getSQL, getSQL, getSQL, getType, isCacheable, isReadOnly, needRecompile, prepare, queryMeta, setCommand, setCurrentRowNumber, setObjectId, setParameterList, setPrepareAlways, setRow, setSession, setSQL, toString, update

Methods inherited from class java.lang.Object

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

Field Detail

limitExpr

protected Expression limitExpr

The limit expression as specified in the LIMIT or TOP clause.

offsetExpr

protected Expression offsetExpr

The offset expression as specified in the LIMIT .. OFFSET clause.

sampleSize

protected int sampleSize

The sample size

distinct

protected boolean distinct

Whether the result must only contain distinct rows.

randomAccessResult

protected boolean randomAccessResult

Whether the result needs to support random access.

Method Detail

queryWithoutCache

protected abstract LocalResult queryWithoutCache(int limit,
                            ResultTarget target)

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.

Parameters:

limit - the limit as specified in the JDBC method call

target - the target to write results to

Returns:

the result

init

public abstract void init()

Initialize the query.

getExpressions

public abstract ArrayList<Expression> getExpressions()

The the list of select expressions. This may include invisible expressions such as order by expressions.

Returns:

the list of expressions

getCost

public abstract double getCost()

Calculate the cost to execute this query.

Returns:

the cost

getCostAsExpression

public int getCostAsExpression()

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.

Returns:

the estimated cost as an integer

getTables

public abstract HashSet<Table> getTables()

Get all tables that are involved in this query.

Returns:

the set of tables

setOrder

public abstract void setOrder(ArrayList<SelectOrderBy> order)

Set the order by list.

Parameters:

order - the order by list

setForUpdate

public abstract void setForUpdate(boolean forUpdate)

Set the 'for update' flag.

Parameters:

forUpdate - the new setting

getColumnCount

public abstract int getColumnCount()

Get the column count of this query.

Returns:

the column count

mapColumns

public abstract void mapColumns(ColumnResolver resolver,
              int level)

Map the columns to the given column resolver.

Parameters:

resolver - the resolver

level - the subquery level (0 is the top level query, 1 is the first subquery level)

setEvaluatable

public abstract void setEvaluatable(TableFilter tableFilter,
                  boolean b)

Change the evaluatable flag. This is used when building the execution plan.

Parameters:

tableFilter - the table filter

b - the new value

addGlobalCondition

public abstract void addGlobalCondition(Parameter param,
                      int columnId,
                      int comparisonType)

Add a condition to the query. This is used for views.

Parameters:

param - the parameter

columnId - the column index (0 meaning the first column)

comparisonType - the comparison type

isEverything

public abstract boolean isEverything(ExpressionVisitor visitor)

Check if this expression and all sub-expressions can fulfill a criteria. If any part returns false, the result is false.

Parameters:

visitor - the visitor

Returns:

if the criteria can be fulfilled

updateAggregate

public abstract void updateAggregate(Session s)

Update all aggregate function values.

Parameters:

s - the session

fireBeforeSelectTriggers

public abstract void fireBeforeSelectTriggers()

Call the before triggers on all tables.

setDistinct

public void setDistinct(boolean b)

Set the distinct flag.

Parameters:

b - the new value

setRandomAccessResult

public void setRandomAccessResult(boolean b)

Whether results need to support random access.

Parameters:

b - the new value

isQuery

public boolean isQuery()

Description copied from class: Prepared

Check if this object is a query.

Overrides:

isQuery in class Prepared

Returns:

true if it is

isTransactional

public boolean isTransactional()

Description copied from class: Prepared

Check if this command is transactional. If it is not, then it forces the current transaction to commit.

Specified by:

isTransactional in class Prepared

Returns:

true if it is

disableCache

public void disableCache()

Disable caching of result sets.

getParameterValues

public final Value[] getParameterValues()

query

public LocalResult query(int maxrows)

Description copied from class: Prepared

Execute the query.

Overrides:

query in class Prepared

Parameters:

maxrows - the maximum number of rows to return

Returns:

the result set

prepareOrder

public SortOrder prepareOrder(ArrayList<SelectOrderBy> orderList,
                     int expressionCount)

Create a SortOrder object given the list of SelectOrderBy objects. The expression list is extended if necessary.

Parameters:

orderList - a list of SelectOrderBy elements

expressionCount - the number of columns in the query

Returns:

the SortOrder object

setOffset

public void setOffset(Expression offset)

setLimit

public void setLimit(Expression limit)

setSampleSize

public void setSampleSize(int sampleSize)

getMaxDataModificationId

public final long getMaxDataModificationId()