ExpressionVisitor

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 and Description
`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.
`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.
`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.
`static int`	`READONLY` Does the expression have no side effects (change the data)?
`static ExpressionVisitor`	`READONLY_VISITOR` The visitor singleton for the type EVALUATABLE.
`static int`	`SET_MAX_DATA_MODIFICATION_ID` Request to set the latest modification id (addDataModificationId).

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`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(AllColumnsForPlan columns)` Create a new visitor to get all referenced columns.
`static ExpressionVisitor`	`getColumnsVisitor(java.util.HashSet<Column> columns, Table table)` 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.
`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.
  - 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.
- 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.
  - 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
  - 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

Method Summary

Methods inherited from class java.lang.Object

Field Detail

INDEPENDENT

INDEPENDENT_VISITOR

OPTIMIZABLE_AGGREGATE

DETERMINISTIC

DETERMINISTIC_VISITOR

EVALUATABLE

EVALUATABLE_VISITOR

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

Method Detail

getDependenciesVisitor

getOptimizableVisitor

getNotFromResolverVisitor

getColumnsVisitor

getColumnsVisitor

getMaxModificationIdVisitor

getDecrementQueryLevelVisitor

addDependency

getDependencies

incrementQueryLevel

getResolver

getColumnResolvers

addDataModificationId

getMaxDataModificationId

getTable

getType

allColumnsForTableFilters