org.h2.expression

Class Subquery

java.lang.Object

org.h2.expression.Expression

org.h2.expression.Subquery

public class Subquery
extends Expression

A query returning a single value. Subqueries are used inside other statements.

Field Summary

Fields inherited from class org.h2.expression.Expression

MAP_IN_AGGREGATE, MAP_IN_WINDOW, MAP_INITIAL

Constructor Summary

Constructors

Constructor and Description
Subquery(Query query)

Method Summary

Methods

Modifier and Type	Method and Description
java.util.ArrayList<Value>	getAllRows(Session session) Evaluates and returns all rows of the subquery.
int	getCost() Estimate the cost to process the expression.
Expression[]	getExpressionColumns(Session session) If this expression consists of column expressions it should return them.
Query	getQuery()
java.lang.StringBuilder	getSQL(java.lang.StringBuilder builder, boolean alwaysQuote) Appends the SQL statement of this expression to the specified builder.
TypeInfo	getType() Returns 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, int state) 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	updateAggregate(Session session, int stage) Update an aggregate value.

Methods inherited from class org.h2.expression.Expression

addFilterConditions, createIndexConditions, getAlias, getBooleanValue, getColumnName, getExpressionColumns, getExpressionColumns, getNonAliasExpression, getNotIfPossible, getNullable, getSchemaName, getSQL, getSubexpression, getSubexpressionCount, getTableAlias, getTableName, getUnenclosedSQL, isAutoIncrement, isConstant, isNullConstant, isValueSet, toString, writeExpressions, writeExpressions

Methods inherited from class java.lang.Object

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

Constructor Detail

Subquery

public Subquery(Query query)

Method Detail

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

getAllRows

public java.util.ArrayList<Value> getAllRows(Session session)

Evaluates and returns all rows of the subquery.

Parameters:

session - the session

Returns:

values in all rows

getType

public TypeInfo getType()

Description copied from class: Expression

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

Specified by:

getType in class Expression

Returns:

the data type

mapColumns

public void mapColumns(ColumnResolver resolver,
              int level,
              int state)

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

state - current state for nesting checks, initial value is Expression.MAP_INITIAL

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

getSQL

public java.lang.StringBuilder getSQL(java.lang.StringBuilder builder,
                             boolean alwaysQuote)

Description copied from class: Expression

Appends the SQL statement of this expression to the specified builder. This may not always be the original SQL statement, specially after optimization.

Specified by:

getSQL in class Expression

Parameters:

builder - string builder

alwaysQuote - quote all identifiers

Returns:

the specified string builder

updateAggregate

public void updateAggregate(Session session,
                   int stage)

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

stage - select stage

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

getQuery

public Query getQuery()

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

getExpressionColumns

public Expression[] getExpressionColumns(Session session)

Description copied from class: Expression

If this expression consists of column expressions it should return them.

Overrides:

getExpressionColumns in class Expression

Parameters:

session - the session

Returns:

array of expression columns if applicable, null otherwise