Class Select

java.lang.Object

org.h2.command.Prepared

org.h2.command.query.Query

org.h2.command.query.Select

public class Select
extends Query

This class represents a simple SELECT statement. For each select statement, visibleColumnCount <= distinctColumnCount <= expressionCount. The expression list count could include ORDER BY and GROUP BY expressions that are not in the select list. The call sequence is init(), mapColumns() if it's a subquery, prepare().

Author:

Thomas Mueller, Joel Turkel (Group sorted query)

Field Summary

Fields inherited from class Prepared

create, parameters, prepareAlways, session, sqlStatement, sqlTokens

Constructor Summary

Constructors

Constructor	Description
Select(SessionLocal session, Select parentSelect)

Method Summary

Modifier and Type	Method	Description
void	addCondition(Expression cond)	Add a condition to the list of conditions.
void	addGlobalCondition(Parameter param, int columnId, int comparisonType)	Add a condition to the query.
void	addTableFilter(TableFilter filter, boolean isTop)	Add a table to the query.
boolean	addWindow(String name, Window window)	Adds a named window definition.
boolean	allowGlobalConditions()	Check whether adding condition to the query is allowed.
void	fireBeforeSelectTriggers()	Call the before triggers on all tables.
Expression	getCondition()
double	getCost()	Calculate the cost to execute this query.
ArrayList<Expression>	getGroupBy()
SelectGroups	getGroupDataIfCurrent(boolean window)	Get the group data if there is currently a group-by active.
Expression	getHaving()
Expression	getIfSingleRow()	If this query is determined as a single-row query, returns a replacement expression.
Select	getParentSelect()	Returns parent select, or null.
String	getPlanSQL(int sqlFlags)	Get the SQL statement with the execution plan.
Expression	getQualify()
SortOrder	getSortOrder()
HashSet<Table>	getTables()	Get all tables that are involved in this query.
ArrayList<TableFilter>	getTopFilters()
TableFilter	getTopTableFilter()
Window	getWindow(String name)	Returns a window with specified name, or null.
void	init()	Initialize the query.
boolean	isAnyDistinct()
boolean	isCacheable()
boolean	isConstantQuery()	Check if this query will always return the same value and has no side effects.
boolean	isEverything(ExpressionVisitor visitor)	Check if this expression and all sub-expressions can fulfill a criteria.
boolean	isGroupQuery()	Checks if this query is a group query.
boolean	isGroupWindowStage2()	Checks if window stage of group window query is performed.
boolean	isQuickAggregateQuery()	Check if this is an aggregate query with direct lookup, for example a query of the type SELECT COUNT(*) FROM TEST or SELECT MAX(ID) FROM TEST.
boolean	isUnion()	Check if this is a UNION query.
boolean	isWindowQuery()	Checks if this query contains window functions.
void	mapColumns(ColumnResolver resolver, int level)	Map the columns to the given column resolver.
void	prepare()	Prepare this statement.
protected ResultInterface	queryWithoutCache(long maxRows, ResultTarget target)	Execute the query without checking the cache.
void	setDistinct()	Set the distinct flag.
void	setDistinct(Expression[] distinctExpressions)	Set the DISTINCT ON expressions.
void	setEvaluatable(TableFilter tableFilter, boolean b)	Change the evaluatable flag.
void	setExplicitTable()	Convert this SELECT to an explicit table (TABLE tableName).
void	setExpressions(ArrayList<Expression> expressions)
void	setForUpdate(boolean b)	Set the 'for update' flag.
void	setGroupBy(ArrayList<Expression> group)
void	setGroupQuery()	Set when SELECT statement contains (non-window) aggregate functions, GROUP BY clause or HAVING clause.
void	setHaving(Expression having)
void	setQualify(Expression qualify)
void	setWildcard()	Sets a wildcard expression as in "SELECT * FROM TEST".
void	setWindowQuery()	Called if this query contains window functions.
void	updateAggregate(SessionLocal s, int stage)	Update all aggregate function values.

Methods inherited from class Query

collectDependencies, disableCache, exists, getColumnCount, getCostAsExpression, getExpressions, getFetch, getMaxDataModificationId, getOffset, getRowDataType, getType, hasOrder, isFetchPercent, isNeverLazy, isQuery, isRandomAccessResult, isReadOnly, isStandardDistinct, isTransactional, isWithTies, query, query, queryMeta, setDistinctIfPossible, setFetch, setFetchPercent, setNeverLazy, setOffset, setOrder, setRandomAccessResult, setWithTies, toTable

Methods inherited from class Prepared

checkCanceled, checkParameters, getCteCleanups, getCurrentRowNumber, getObjectId, getParameters, getPersistedObjectId, getSession, getSimpleSQL, getSQL, getSQLTokens, needRecompile, setCommand, setCteCleanups, setCurrentRowNumber, setParameterList, setPersistedObjectId, setPrepareAlways, setRow, setSession, setSQL, toString, update

Methods inherited from class Object

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

Constructor Details

Select

public Select(SessionLocal session,
 Select parentSelect)

Method Details

isUnion

public boolean isUnion()

Description copied from class: Query

Check if this is a UNION query.

Specified by:

isUnion in class Query

Returns:

true if this is a UNION query

addTableFilter

public void addTableFilter(TableFilter filter,
 boolean isTop)

Add a table to the query.

Parameters:

filter - the table to add

isTop - if the table can be the first table in the query plan

getTopFilters

public ArrayList<TableFilter> getTopFilters()

setExpressions

public void setExpressions(ArrayList<Expression> expressions)

setExplicitTable

public void setExplicitTable()

Convert this SELECT to an explicit table (TABLE tableName).

setWildcard

public void setWildcard()

Sets a wildcard expression as in "SELECT * FROM TEST".

setGroupQuery

public void setGroupQuery()

Set when SELECT statement contains (non-window) aggregate functions, GROUP BY clause or HAVING clause.

setWindowQuery

public void setWindowQuery()

Called if this query contains window functions.

setGroupBy

public void setGroupBy(ArrayList<Expression> group)

getGroupBy

public ArrayList<Expression> getGroupBy()

getGroupDataIfCurrent

public SelectGroups getGroupDataIfCurrent(boolean window)

Get the group data if there is currently a group-by active.

Parameters:

window - is this a window function

Returns:

the grouped data

setDistinct

public void setDistinct()

Set the distinct flag.

setDistinct

public void setDistinct(Expression[] distinctExpressions)

Set the DISTINCT ON expressions.

Parameters:

distinctExpressions - array of expressions

isAnyDistinct

public boolean isAnyDistinct()

Overrides:

isAnyDistinct in class Query

Returns:

whether this query is a DISTINCT or DISTINCT ON (...) query

addWindow

public boolean addWindow(String name,
 Window window)

Adds a named window definition.

Parameters:

name - name

window - window definition

Returns:

true if a new definition was added, false if old definition was replaced

getWindow

public Window getWindow(String name)

Returns a window with specified name, or null.

Parameters:

name - name of the window

Returns:

the window with specified name, or null

addCondition

public void addCondition(Expression cond)

Add a condition to the list of conditions.

Parameters:

cond - the condition to add

getCondition

public Expression getCondition()

queryWithoutCache

protected ResultInterface queryWithoutCache(long maxRows,
 ResultTarget target)

Description copied from class: Query

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.

Specified by:

queryWithoutCache in class Query

Parameters:

maxRows - the limit as specified in the JDBC method call

target - the target to write results to

Returns:

the result

init

public void init()

Description copied from class: Query

Initialize the query.

Specified by:

init in class Query

prepare

public void prepare()

Description copied from class: Prepared

Prepare this statement.

Overrides:

prepare in class Prepared

getCost

public double getCost()

Description copied from class: Query

Calculate the cost to execute this query.

Specified by:

getCost in class Query

Returns:

the cost

getTables

public HashSet<Table> getTables()

Description copied from class: Query

Get all tables that are involved in this query.

Specified by:

getTables in class Query

Returns:

the set of tables

fireBeforeSelectTriggers

public void fireBeforeSelectTriggers()

Description copied from class: Query

Call the before triggers on all tables.

Specified by:

fireBeforeSelectTriggers in class Query

getPlanSQL

public String getPlanSQL(int sqlFlags)

Description copied from class: Prepared

Get the SQL statement with the execution plan.

Overrides:

getPlanSQL in class Prepared

Parameters:

sqlFlags - formatting flags

Returns:

the execution plan

setHaving

public void setHaving(Expression having)

getHaving

public Expression getHaving()

setQualify

public void setQualify(Expression qualify)

getQualify

public Expression getQualify()

getTopTableFilter

public TableFilter getTopTableFilter()

setForUpdate

public void setForUpdate(boolean b)

Description copied from class: Query

Set the 'for update' flag.

Specified by:

setForUpdate in class Query

Parameters:

b - the new setting

mapColumns

public void mapColumns(ColumnResolver resolver,
 int level)

Description copied from class: Query

Map the columns to the given column resolver.

Specified by:

mapColumns in class Query

Parameters:

resolver - the resolver

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

setEvaluatable

public void setEvaluatable(TableFilter tableFilter,
 boolean b)

Description copied from class: Query

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

Specified by:

setEvaluatable in class Query

Parameters:

tableFilter - the table filter

b - the new value

isQuickAggregateQuery

public boolean isQuickAggregateQuery()

Check if this is an aggregate query with direct lookup, for example a query of the type SELECT COUNT(*) FROM TEST or SELECT MAX(ID) FROM TEST.

Returns:

true if a direct lookup is possible

isGroupQuery

public boolean isGroupQuery()

Checks if this query is a group query.

Returns:

whether this query is a group query.

isWindowQuery

public boolean isWindowQuery()

Checks if this query contains window functions.

Returns:

whether this query contains window functions

isGroupWindowStage2

public boolean isGroupWindowStage2()

Checks if window stage of group window query is performed. If true, column resolver may not be used.

Returns:

true if window stage of group window query is performed

addGlobalCondition

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

Description copied from class: Query

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

Specified by:

addGlobalCondition in class Query

Parameters:

param - the parameter

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

comparisonType - the comparison type

updateAggregate

public void updateAggregate(SessionLocal s,
 int stage)

Description copied from class: Query

Update all aggregate function values.

Specified by:

updateAggregate in class Query

Parameters:

s - the session

stage - select stage

isEverything

public boolean isEverything(ExpressionVisitor visitor)

Description copied from class: Query

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

Specified by:

isEverything in class Query

Parameters:

visitor - the visitor

Returns:

if the criteria can be fulfilled

isCacheable

public boolean isCacheable()

Overrides:

isCacheable in class Prepared

allowGlobalConditions

public boolean allowGlobalConditions()

Description copied from class: Query

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.

Specified by:

allowGlobalConditions in class Query

Returns:

true if adding global conditions is allowed

getSortOrder

public SortOrder getSortOrder()

getParentSelect

public Select getParentSelect()

Returns parent select, or null.

Returns:

parent select, or null

isConstantQuery

public boolean isConstantQuery()

Description copied from class: Query

Check if this query will always return the same value and has no side effects.

Overrides:

isConstantQuery in class Query

Returns:

if this query will always return the same value and has no side effects.

getIfSingleRow

public Expression getIfSingleRow()

Description copied from class: Query

If this query is determined as a single-row query, returns a replacement expression.

Overrides:

getIfSingleRow in class Query

Returns:

the expression, or null