java.lang.Object
- org.h2.expression.ExpressionVisitor

```
public final class ExpressionVisitor
extends java.lang.Object
```
The visitor pattern is used to iterate through all expressions of a query to optimize a statement.

Field Summary

Fields
Modifier and Type	Field	Description
`private static int`	`CACHED`	Count of cached INDEPENDENT and EVALUATABLE visitors with different query level.
`private AllColumnsForPlan`	`columns1`
`static int`	`DECREMENT_QUERY_LEVEL`	Decrement query level of all expression columns.
`static int`	`DETERMINISTIC`	Does the expression return the same results for the same parameters?
`static ExpressionVisitor`	`DETERMINISTIC_VISITOR`	The visitor singleton for the type DETERMINISTIC.
`static int`	`EVALUATABLE`	Can the expression be evaluated, that means are all columns set to 'evaluatable'?
`static ExpressionVisitor`	`EVALUATABLE_VISITOR`	The visitor singleton for the type EVALUATABLE.
`private static ExpressionVisitor[]`	`EVALUATABLE_VISITORS`	EVALUATABLE listeners with query level 0, 1, ...
`static int`	`GET_COLUMNS1`	Get all referenced columns for the optimiser.
`static int`	`GET_COLUMNS2`	Get all referenced columns.
`static int`	`GET_DEPENDENCIES`	Request to get the set of dependencies (addDependency).
`static int`	`INDEPENDENT`	Is the value independent on unset parameters or on columns of a higher level query, or sequence values (that means can it be evaluated right now)?
`static ExpressionVisitor`	`INDEPENDENT_VISITOR`	The visitor singleton for the type INDEPENDENT.
`private static ExpressionVisitor[]`	`INDEPENDENT_VISITORS`	INDEPENDENT listeners with query level 0, 1, ...
`private long[]`	`maxDataModificationId`
`static int`	`NOT_FROM_RESOLVER`	Does an expression have no relation to the given table filter (getResolver)?
`static int`	`OPTIMIZABLE_AGGREGATE`	Are all aggregates MIN(column), MAX(column), COUNT(*), MEDIAN(column), ENVELOPE(count) for the given table (getTable)?
`static int`	`QUERY_COMPARABLE`	Can the expression be added to a condition of an outer query.
`static ExpressionVisitor`	`QUERY_COMPARABLE_VISITOR`	The visitor singleton for the type QUERY_COMPARABLE.
`private int`	`queryLevel`
`static int`	`READONLY`	Does the expression have no side effects (change the data)?
`static ExpressionVisitor`	`READONLY_VISITOR`	The visitor singleton for the type EVALUATABLE.
`private ColumnResolver`	`resolver`
`private java.util.HashSet<?>`	`set`
`static int`	`SET_MAX_DATA_MODIFICATION_ID`	Request to set the latest modification id (addDataModificationId).
`private Table`	`table`
`private int`	`type`

Constructor Summary

Constructors
Modifier	Constructor	Description
`private`	`ExpressionVisitor(int type)`
`private`	`ExpressionVisitor(int type, int queryLevel)`
`private`	`ExpressionVisitor(int type, int queryLevel, java.util.HashSet<?> set, AllColumnsForPlan columns1, Table table, ColumnResolver resolver, long[] maxDataModificationId)`

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`(package private) void`	`addColumn1(Column column)`	Add a new column to the set of columns.
`(package private) void`	`addColumn2(Column column)`	Add a new column to the set of columns.
`void`	`addDataModificationId(long value)`	Update the field maxDataModificationId if this value is higher than the current value.
`void`	`addDependency(DbObject obj)`	Add a new dependency to the set of dependencies.
`static void`	`allColumnsForTableFilters(TableFilter[] filters, AllColumnsForPlan allColumnsSet)`	Get the set of columns of all tables.
`java.util.HashSet<ColumnResolver>`	`getColumnResolvers()`	Get the set of column resolvers.
`static ExpressionVisitor`	`getColumnsVisitor(java.util.HashSet<Column> columns, Table table)`	Create a new visitor to get all referenced columns.
`static ExpressionVisitor`	`getColumnsVisitor(AllColumnsForPlan columns)`	Create a new visitor to get all referenced columns.
`static ExpressionVisitor`	`getDecrementQueryLevelVisitor(java.util.HashSet<ColumnResolver> columnResolvers, int queryDecrement)`	Create a new visitor to decrement query level in columns with the specified resolvers.
`java.util.HashSet<DbObject>`	`getDependencies()`	Get the dependency set.
`static ExpressionVisitor`	`getDependenciesVisitor(java.util.HashSet<DbObject> dependencies)`	Create a new visitor object to collect dependencies.
`long`	`getMaxDataModificationId()`	Get the last data modification.
`static ExpressionVisitor`	`getMaxModificationIdVisitor()`
`static ExpressionVisitor`	`getNotFromResolverVisitor(ColumnResolver resolver)`	Create a new visitor to check if no expression depends on the given resolver.
`static ExpressionVisitor`	`getOptimizableVisitor(Table table)`	Create a new visitor to check if all aggregates are for the given table.
`(package private) int`	`getQueryLevel()`
`ColumnResolver`	`getResolver()`	Get the column resolver.
`Table`	`getTable()`	Get the table.
`int`	`getType()`	Get the visitor type.
`ExpressionVisitor`	`incrementQueryLevel(int offset)`	Increment or decrement the query level.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - INDEPENDENT
```
public static final int INDEPENDENT
```
    Is the value independent on unset parameters or on columns of a higher level query, or sequence values (that means can it be evaluated right now)?
    
    See Also:
    
    Constant Field Values
  - INDEPENDENT_VISITOR
```
public static final ExpressionVisitor INDEPENDENT_VISITOR
```
    The visitor singleton for the type INDEPENDENT.
  - OPTIMIZABLE_AGGREGATE
```
public static final int OPTIMIZABLE_AGGREGATE
```
    Are all aggregates MIN(column), MAX(column), COUNT(*), MEDIAN(column), ENVELOPE(count) for the given table (getTable)?
    
    See Also:
    
    Constant Field Values
  - DETERMINISTIC
```
public static final int DETERMINISTIC
```
    Does the expression return the same results for the same parameters?
    
    See Also:
    
    Constant Field Values
  - DETERMINISTIC_VISITOR
```
public static final ExpressionVisitor DETERMINISTIC_VISITOR
```
    The visitor singleton for the type DETERMINISTIC.
  - EVALUATABLE
```
public static final int EVALUATABLE
```
    Can the expression be evaluated, that means are all columns set to 'evaluatable'?
    
    See Also:
    
    Constant Field Values
  - EVALUATABLE_VISITOR
```
public static final ExpressionVisitor EVALUATABLE_VISITOR
```
    The visitor singleton for the type EVALUATABLE.
  - CACHED
```
private static final int CACHED
```
    Count of cached INDEPENDENT and EVALUATABLE visitors with different query level.
    
    See Also:
    
    Constant Field Values
  - INDEPENDENT_VISITORS
```
private static final ExpressionVisitor[] INDEPENDENT_VISITORS
```
    INDEPENDENT listeners with query level 0, 1, ...
  - EVALUATABLE_VISITORS
```
private static final ExpressionVisitor[] EVALUATABLE_VISITORS
```
    EVALUATABLE listeners with query level 0, 1, ...
  - SET_MAX_DATA_MODIFICATION_ID
```
public static final int SET_MAX_DATA_MODIFICATION_ID
```
    Request to set the latest modification id (addDataModificationId).
    
    See Also:
    
    Constant Field Values
  - READONLY
```
public static final int READONLY
```
    Does the expression have no side effects (change the data)?
    
    See Also:
    
    Constant Field Values
  - READONLY_VISITOR
```
public static final ExpressionVisitor READONLY_VISITOR
```
    The visitor singleton for the type EVALUATABLE.
  - NOT_FROM_RESOLVER
```
public static final int NOT_FROM_RESOLVER
```
    Does an expression have no relation to the given table filter (getResolver)?
    
    See Also:
    
    Constant Field Values
  - GET_DEPENDENCIES
```
public static final int GET_DEPENDENCIES
```
    Request to get the set of dependencies (addDependency).
    
    See Also:
    
    Constant Field Values
  - QUERY_COMPARABLE
```
public static final int QUERY_COMPARABLE
```
    Can the expression be added to a condition of an outer query. Example: ROWNUM() can't be added as a condition to the inner query of select id from (select t.*, rownum as r from test t) where r between 2 and 3; Also a sequence expression must not be used.
    
    See Also:
    
    Constant Field Values
  - GET_COLUMNS1
```
public static final int GET_COLUMNS1
```
    Get all referenced columns for the optimiser.
    
    See Also:
    
    Constant Field Values
  - GET_COLUMNS2
```
public static final int GET_COLUMNS2
```
    Get all referenced columns.
    
    See Also:
    
    Constant Field Values
  - DECREMENT_QUERY_LEVEL
```
public static final int DECREMENT_QUERY_LEVEL
```
    Decrement query level of all expression columns.
    
    See Also:
    
    Constant Field Values
  - QUERY_COMPARABLE_VISITOR
```
public static final ExpressionVisitor QUERY_COMPARABLE_VISITOR
```
    The visitor singleton for the type QUERY_COMPARABLE.
  - type
```
private final int type
```
  - queryLevel
```
private final int queryLevel
```
  - set
```
private final java.util.HashSet<?> set
```
  - columns1
```
private final AllColumnsForPlan columns1
```
  - table
```
private final Table table
```
  - maxDataModificationId
```
private final long[] maxDataModificationId
```
  - resolver
```
private final ColumnResolver resolver
```
- Constructor Detail
  - ExpressionVisitor
```
private ExpressionVisitor(int type,
                          int queryLevel,
                          java.util.HashSet<?> set,
                          AllColumnsForPlan columns1,
                          Table table,
                          ColumnResolver resolver,
                          long[] maxDataModificationId)
```
  - ExpressionVisitor
```
private ExpressionVisitor(int type)
```
  - ExpressionVisitor
```
private ExpressionVisitor(int type,
                          int queryLevel)
```
- Method Detail
  - getDependenciesVisitor
```
public static ExpressionVisitor getDependenciesVisitor(java.util.HashSet<DbObject> dependencies)
```
    Create a new visitor object to collect dependencies.
    
    Parameters:
    
    dependencies - the dependencies set
    
    Returns:
    
    the new visitor
  - getOptimizableVisitor
```
public static ExpressionVisitor getOptimizableVisitor(Table table)
```
    Create a new visitor to check if all aggregates are for the given table.
    
    Parameters:
    
    table - the table
    
    Returns:
    
    the new visitor
  - getNotFromResolverVisitor
```
public static ExpressionVisitor getNotFromResolverVisitor(ColumnResolver resolver)
```
    Create a new visitor to check if no expression depends on the given resolver.
    
    Parameters:
    
    resolver - the resolver
    
    Returns:
    
    the new visitor
  - getColumnsVisitor
```
public static ExpressionVisitor getColumnsVisitor(AllColumnsForPlan columns)
```
    Create a new visitor to get all referenced columns.
    
    Parameters:
    
    columns - the columns map
    
    Returns:
    
    the new visitor
  - getColumnsVisitor
```
public static ExpressionVisitor getColumnsVisitor(java.util.HashSet<Column> columns,
                                                  Table table)
```
    Create a new visitor to get all referenced columns.
    
    Parameters:
    
    columns - the columns map
    
    table - table to gather columns from, or null to gather all columns
    
    Returns:
    
    the new visitor
  - getMaxModificationIdVisitor
```
public static ExpressionVisitor getMaxModificationIdVisitor()
```
  - getDecrementQueryLevelVisitor
```
public static ExpressionVisitor getDecrementQueryLevelVisitor(java.util.HashSet<ColumnResolver> columnResolvers,
                                                              int queryDecrement)
```
    Create a new visitor to decrement query level in columns with the specified resolvers.
    
    Parameters:
    
    columnResolvers - column resolvers
    
    queryDecrement - 0 to check whether operation is allowed, 1 to actually perform the decrement
    
    Returns:
    
    the new visitor
  - addDependency
```
public void addDependency(DbObject obj)
```
    Add a new dependency to the set of dependencies. This is used for GET_DEPENDENCIES visitors.
    
    Parameters:
    
    obj - the additional dependency.
  - addColumn1
```
void addColumn1(Column column)
```
    Add a new column to the set of columns. This is used for GET_COLUMNS visitors.
    
    Parameters:
    
    column - the additional column.
  - addColumn2
```
void addColumn2(Column column)
```
    Add a new column to the set of columns. This is used for GET_COLUMNS2 visitors.
    
    Parameters:
    
    column - the additional column.
  - getDependencies
```
public java.util.HashSet<DbObject> getDependencies()
```
    Get the dependency set. This is used for GET_DEPENDENCIES visitors.
    
    Returns:
    
    the set
  - incrementQueryLevel
```
public ExpressionVisitor incrementQueryLevel(int offset)
```
    Increment or decrement the query level.
    
    Parameters:
    
    offset - 1 to increment, -1 to decrement
    
    Returns:
    
    this visitor or its clone with the changed query level
  - getResolver
```
public ColumnResolver getResolver()
```
    Get the column resolver. This is used for NOT_FROM_RESOLVER visitors.
    
    Returns:
    
    the column resolver
  - getColumnResolvers
```
public java.util.HashSet<ColumnResolver> getColumnResolvers()
```
    Get the set of column resolvers. This is used for DECREMENT_QUERY_LEVEL visitors.
    
    Returns:
    
    the set
  - addDataModificationId
```
public void addDataModificationId(long value)
```
    Update the field maxDataModificationId if this value is higher than the current value. This is used for SET_MAX_DATA_MODIFICATION_ID visitors.
    
    Parameters:
    
    value - the data modification id
  - getMaxDataModificationId
```
public long getMaxDataModificationId()
```
    Get the last data modification. This is used for SET_MAX_DATA_MODIFICATION_ID visitors.
    
    Returns:
    
    the maximum modification id
  - getQueryLevel
```
int getQueryLevel()
```
  - getTable
```
public Table getTable()
```
    Get the table. This is used for OPTIMIZABLE_MIN_MAX_COUNT_ALL visitors.
    
    Returns:
    
    the table
  - getType
```
public int getType()
```
    Get the visitor type.
    
    Returns:
    
    the type
  - allColumnsForTableFilters
```
public static void allColumnsForTableFilters(TableFilter[] filters,
                                             AllColumnsForPlan allColumnsSet)
```
    Get the set of columns of all tables.
    
    Parameters:
    
    filters - the filters
    
    allColumnsSet - the on-demand all-columns set

Class ExpressionVisitor

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

INDEPENDENT

INDEPENDENT_VISITOR

OPTIMIZABLE_AGGREGATE

DETERMINISTIC

DETERMINISTIC_VISITOR

EVALUATABLE

EVALUATABLE_VISITOR

CACHED

INDEPENDENT_VISITORS

EVALUATABLE_VISITORS

SET_MAX_DATA_MODIFICATION_ID

READONLY

READONLY_VISITOR

NOT_FROM_RESOLVER

GET_DEPENDENCIES

QUERY_COMPARABLE

GET_COLUMNS1

GET_COLUMNS2

DECREMENT_QUERY_LEVEL

QUERY_COMPARABLE_VISITOR

type

queryLevel

set

columns1

table

maxDataModificationId

resolver

Constructor Detail

ExpressionVisitor

ExpressionVisitor

ExpressionVisitor

Method Detail

getDependenciesVisitor

getOptimizableVisitor

getNotFromResolverVisitor

getColumnsVisitor

getColumnsVisitor

getMaxModificationIdVisitor

getDecrementQueryLevelVisitor

addDependency

addColumn1

addColumn2

getDependencies

incrementQueryLevel

getResolver

getColumnResolvers

addDataModificationId

getMaxDataModificationId

getQueryLevel

getTable

getType

allColumnsForTableFilters