org.h2.expression

Class Aggregate

java.lang.Object

org.h2.expression.Expression

org.h2.expression.Aggregate

public class Aggregate
extends Expression

Implements the integrated aggregate functions, such as COUNT, MAX, SUM.

Field Summary

Fields

Modifier and Type	Field and Description
static int	COUNT The aggregate type for COUNT(expression).
static int	COUNT_ALL The aggregate type for COUNT(*).
static int	GROUP_CONCAT The aggregate type for GROUP_CONCAT(...).

Constructor Summary

Constructors

Constructor and Description
Aggregate(int type, Expression on, Select select, boolean distinct) Create a new aggregate object.

Method Summary

Methods

Modifier and Type	Method and Description
static int	getAggregateType(String name) Get the aggregate type for this name, or -1 if no aggregate has been found.
int	getCost() Estimate the cost to process the expression.
int	getDisplaySize() Get the display size of this expression.
long	getPrecision() Get the precision of this expression.
int	getScale() Get the scale of this expression.
String	getSQL() Get the SQL statement of this expression.
int	getType() Return the data type.
Value	getValue(Session session) Return the resulting value for the current row.
boolean	isEverything(ExpressionVisitor visitor) Check if this expression and all sub-expressions can fulfill a criteria.
void	mapColumns(ColumnResolver resolver, int level) Map the columns of the resolver to expression columns.
Expression	optimize(Session session) Try to optimize the expression.
void	setEvaluatable(TableFilter tableFilter, boolean b) Tell the expression columns whether the table filter can return values now.
void	setOrder(ArrayList<SelectOrderBy> orderBy) Set the order for GROUP_CONCAT.
void	setSeparator(Expression separator) Set the separator for GROUP_CONCAT.
void	updateAggregate(Session session) Update an aggregate value.

Methods inherited from class org.h2.expression.Expression

addFilterConditions, createIndexConditions, getAlias, getBooleanValue, getColumnName, getExpressionColumns, getExpressionColumns, getNonAliasExpression, getNotIfPossible, getNullable, getSchemaName, getTableAlias, getTableName, isAutoIncrement, isConstant, isValueSet, isWildcard, toString

Methods inherited from class java.lang.Object

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

Field Detail

COUNT_ALL

public static final int COUNT_ALL

The aggregate type for COUNT(*).

See Also:

Constant Field Values

COUNT

public static final int COUNT

The aggregate type for COUNT(expression).

See Also:

Constant Field Values

GROUP_CONCAT

public static final int GROUP_CONCAT

The aggregate type for GROUP_CONCAT(...).

See Also:

Constant Field Values

Constructor Detail

Aggregate

public Aggregate(int type,
         Expression on,
         Select select,
         boolean distinct)

Create a new aggregate object.

Parameters:

type - the aggregate type

on - the aggregated expression

select - the select statement

distinct - if distinct is used

Method Detail

getAggregateType

public static int getAggregateType(String name)

Get the aggregate type for this name, or -1 if no aggregate has been found.

Parameters:

name - the aggregate function name

Returns:

-1 if no aggregate function has been found, or the aggregate type

setOrder

public void setOrder(ArrayList<SelectOrderBy> orderBy)

Set the order for GROUP_CONCAT.

Parameters:

orderBy - the order by list

setSeparator

public void setSeparator(Expression separator)

Set the separator for GROUP_CONCAT.

Parameters:

separator - the separator expression

updateAggregate

public void updateAggregate(Session session)

Description copied from class: Expression

Update an aggregate value. This method is called at statement execution time. It is usually called once for each row, but if the expression is used multiple times (for example in the column list, and as part of the HAVING expression) it is called multiple times - the row counter needs to be used to make sure the internal state is only updated once.

Specified by:

updateAggregate in class Expression

Parameters:

session - the session

getValue

public Value getValue(Session session)

Description copied from class: Expression

Return the resulting value for the current row.

Specified by:

getValue in class Expression

Parameters:

session - the session

Returns:

the result

getType

public int getType()

Description copied from class: Expression

Return the data type. The data type may not be known before the optimization phase.

Specified by:

getType in class Expression

Returns:

the type

mapColumns

public void mapColumns(ColumnResolver resolver,
              int level)

Description copied from class: Expression

Map the columns of the resolver to expression columns.

Specified by:

mapColumns in class Expression

Parameters:

resolver - the column resolver

level - the subquery nesting level

optimize

public Expression optimize(Session session)

Description copied from class: Expression

Try to optimize the expression.

Specified by:

optimize in class Expression

Parameters:

session - the session

Returns:

the optimized expression

setEvaluatable

public void setEvaluatable(TableFilter tableFilter,
                  boolean b)

Description copied from class: Expression

Tell the expression columns whether the table filter can return values now. This is used when optimizing the query.

Specified by:

setEvaluatable in class Expression

Parameters:

tableFilter - the table filter

b - true if the table filter can return value

getScale

public int getScale()

Description copied from class: Expression

Get the scale of this expression.

Specified by:

getScale in class Expression

Returns:

the scale

getPrecision

public long getPrecision()

Description copied from class: Expression

Get the precision of this expression.

Specified by:

getPrecision in class Expression

Returns:

the precision

getDisplaySize

public int getDisplaySize()

Description copied from class: Expression

Get the display size of this expression.

Specified by:

getDisplaySize in class Expression

Returns:

the display size

getSQL

public String getSQL()

Description copied from class: Expression

Get the SQL statement of this expression. This may not always be the original SQL statement, specially after optimization.

Specified by:

getSQL in class Expression

Returns:

the SQL statement

isEverything

public boolean isEverything(ExpressionVisitor visitor)

Description copied from class: Expression

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 Expression

Parameters:

visitor - the visitor

Returns:

if the criteria can be fulfilled

getCost

public int getCost()

Description copied from class: Expression

Estimate the cost to process the expression. Used when optimizing the query, to calculate the query plan with the lowest estimated cost.

Specified by:

getCost in class Expression

Returns:

the estimated cost