Expression

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

Direct Known Subclasses:

Aggregate, Alias, CompareLike, Comparison, ConditionAndOr, ConditionExists, ConditionIn, ConditionInConstantSet, ConditionInParameter, ConditionInSelect, ConditionNot, ExpressionColumn, ExpressionList, Function, JavaAggregate, JavaFunction, Operation, Parameter, Rownum, SequenceValue, Subquery, ValueExpression, Variable, Wildcard
```
public abstract class Expression
extends java.lang.Object
```
An expression is a operation, a value, or a function in a query.

Constructor Summary

Constructors
Constructor and Description

Expression()

Constructors
Constructor and Description
`Expression()`

Method Summary

All Methods Static Methods Instance Methods Abstract Methods Concrete Methods
Modifier and Type	Method and Description
`void`	`addFilterConditions(TableFilter filter, boolean outerJoin)` Add conditions to a table filter if they can be evaluated.
`void`	`createIndexConditions(Session session, TableFilter filter)` Create index conditions if possible and attach them to the table filter.
`java.lang.String`	`getAlias()` Get the alias name of a column or SQL expression if it is not an aliased expression.
`boolean`	`getBooleanValue(Session session)` Get the value in form of a boolean expression.
`java.lang.String`	`getColumnName()` Get the column name or alias name of this expression.
`abstract int`	`getCost()` Estimate the cost to process the expression.
`abstract int`	`getDisplaySize()` Get the display size of this expression.
`Expression[]`	`getExpressionColumns(Session session)` If this expression consists of column expressions it should return them.
`static Expression[]`	`getExpressionColumns(Session session, java.sql.ResultSet rs)` Extracts expression columns from the given result set.
`Expression`	`getNonAliasExpression()` Returns the main expression, skipping aliases.
`Expression`	`getNotIfPossible(Session session)` If it is possible, return the negated expression.
`int`	`getNullable()` Check whether this expression is a column and can store NULL.
`abstract long`	`getPrecision()` Get the precision of this expression.
`abstract int`	`getScale()` Get the scale of this expression.
`java.lang.String`	`getSchemaName()` Get the schema name, or null
`abstract java.lang.String`	`getSQL()` Get the SQL statement of this expression.
`java.lang.String`	`getTableAlias()` Get the table alias name or null if this expression does not represent a column.
`java.lang.String`	`getTableName()` Get the table name, or null
`abstract int`	`getType()` Return the data type.
`abstract Value`	`getValue(Session session)` Return the resulting value for the current row.
`boolean`	`isAutoIncrement()` Check if this is an auto-increment column.
`boolean`	`isConstant()` Check if this expression will always return the same value.
`abstract boolean`	`isEverything(ExpressionVisitor visitor)` Check if this expression and all sub-expressions can fulfill a criteria.
`boolean`	`isValueSet()` Is the value of a parameter set.
`boolean`	`isWildcard()` Only returns true if the expression is a wildcard.
`abstract void`	`mapColumns(ColumnResolver resolver, int level)` Map the columns of the resolver to expression columns.
`abstract Expression`	`optimize(Session session)` Try to optimize the expression.
`abstract void`	`setEvaluatable(TableFilter tableFilter, boolean value)` Tell the expression columns whether the table filter can return values now.
`java.lang.String`	`toString()` Convert this expression to a String.
`abstract void`	`updateAggregate(Session session)` Update an aggregate value.

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

- Constructor Detail
  - Expression
```
public Expression()
```
- Method Detail
  - getValue
```
public abstract Value getValue(Session session)
```
    Return the resulting value for the current row.
    
    Parameters:
    
    session - the session
    
    Returns:
    
    the result
  - getType
```
public abstract int getType()
```
    Return the data type. The data type may not be known before the optimization phase.
    
    Returns:
    
    the type
  - mapColumns
```
public abstract void mapColumns(ColumnResolver resolver,
                                int level)
```
    Map the columns of the resolver to expression columns.
    
    Parameters:
    
    resolver - the column resolver
    
    level - the subquery nesting level
  - optimize
```
public abstract Expression optimize(Session session)
```
    Try to optimize the expression.
    
    Parameters:
    
    session - the session
    
    Returns:
    
    the optimized expression
  - setEvaluatable
```
public abstract void setEvaluatable(TableFilter tableFilter,
                                    boolean value)
```
    Tell the expression columns whether the table filter can return values now. This is used when optimizing the query.
    
    Parameters:
    
    tableFilter - the table filter
    
    value - true if the table filter can return value
  - getScale
```
public abstract int getScale()
```
    Get the scale of this expression.
    
    Returns:
    
    the scale
  - getPrecision
```
public abstract long getPrecision()
```
    Get the precision of this expression.
    
    Returns:
    
    the precision
  - getDisplaySize
```
public abstract int getDisplaySize()
```
    Get the display size of this expression.
    
    Returns:
    
    the display size
  - getSQL
```
public abstract java.lang.String getSQL()
```
    Get the SQL statement of this expression. This may not always be the original SQL statement, specially after optimization.
    
    Returns:
    
    the SQL statement
  - updateAggregate
```
public abstract void updateAggregate(Session session)
```
    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.
    
    Parameters:
    
    session - the session
  - isEverything
```
public abstract boolean isEverything(ExpressionVisitor visitor)
```
    Check if this expression and all sub-expressions can fulfill a criteria. If any part returns false, the result is false.
    
    Parameters:
    
    visitor - the visitor
    
    Returns:
    
    if the criteria can be fulfilled
  - getCost
```
public abstract int getCost()
```
    Estimate the cost to process the expression. Used when optimizing the query, to calculate the query plan with the lowest estimated cost.
    
    Returns:
    
    the estimated cost
  - getNotIfPossible
```
public Expression getNotIfPossible(Session session)
```
    If it is possible, return the negated expression. This is used to optimize NOT expressions: NOT ID>10 can be converted to ID<=10. Returns null if negating is not possible.
    
    Parameters:
    
    session - the session
    
    Returns:
    
    the negated expression, or null
  - isConstant
```
public boolean isConstant()
```
    Check if this expression will always return the same value.
    
    Returns:
    
    if the expression is constant
  - isValueSet
```
public boolean isValueSet()
```
    Is the value of a parameter set.
    
    Returns:
    
    true if set
  - isAutoIncrement
```
public boolean isAutoIncrement()
```
    Check if this is an auto-increment column.
    
    Returns:
    
    true if it is an auto-increment column
  - getBooleanValue
```
public boolean getBooleanValue(Session session)
```
    Get the value in form of a boolean expression. Returns true or false. In this database, everything can be a condition.
    
    Parameters:
    
    session - the session
    
    Returns:
    
    the result
  - createIndexConditions
```
public void createIndexConditions(Session session,
                                  TableFilter filter)
```
    Create index conditions if possible and attach them to the table filter.
    
    Parameters:
    
    session - the session
    
    filter - the table filter
  - getColumnName
```
public java.lang.String getColumnName()
```
    Get the column name or alias name of this expression.
    
    Returns:
    
    the column name
  - getSchemaName
```
public java.lang.String getSchemaName()
```
    Get the schema name, or null
    
    Returns:
    
    the schema name
  - getTableName
```
public java.lang.String getTableName()
```
    Get the table name, or null
    
    Returns:
    
    the table name
  - getNullable
```
public int getNullable()
```
    Check whether this expression is a column and can store NULL.
    
    Returns:
    
    whether NULL is allowed
  - getTableAlias
```
public java.lang.String getTableAlias()
```
    Get the table alias name or null if this expression does not represent a column.
    
    Returns:
    
    the table alias name
  - getAlias
```
public java.lang.String getAlias()
```
    Get the alias name of a column or SQL expression if it is not an aliased expression.
    
    Returns:
    
    the alias name
  - isWildcard
```
public boolean isWildcard()
```
    Only returns true if the expression is a wildcard.
    
    Returns:
    
    if this expression is a wildcard
  - getNonAliasExpression
```
public Expression getNonAliasExpression()
```
    Returns the main expression, skipping aliases.
    
    Returns:
    
    the expression
  - addFilterConditions
```
public void addFilterConditions(TableFilter filter,
                                boolean outerJoin)
```
    Add conditions to a table filter if they can be evaluated.
    
    Parameters:
    
    filter - the table filter
    
    outerJoin - if the expression is part of an outer join
  - toString
```
public java.lang.String toString()
```
    Convert this expression to a String.
    
    Overrides:
    
    toString in class java.lang.Object
    
    Returns:
    
    the string representation
  - getExpressionColumns
```
public Expression[] getExpressionColumns(Session session)
```
    If this expression consists of column expressions it should return them.
    
    Parameters:
    
    session - the session
    
    Returns:
    
    array of expression columns if applicable, null otherwise
  - getExpressionColumns
```
public static Expression[] getExpressionColumns(Session session,
                                                java.sql.ResultSet rs)
```
    Extracts expression columns from the given result set.
    
    Parameters:
    
    session - the session
    
    rs - the result set
    
    Returns:
    
    an array of expression columns

Class Expression

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

Expression

Method Detail

getValue

getType

mapColumns

optimize

setEvaluatable

getScale

getPrecision

getDisplaySize

getSQL

updateAggregate

isEverything

getCost

getNotIfPossible

isConstant

isValueSet

isAutoIncrement

getBooleanValue

createIndexConditions

getColumnName

getSchemaName

getTableName

getNullable

getTableAlias

getAlias

isWildcard

getNonAliasExpression

addFilterConditions

toString

getExpressionColumns

getExpressionColumns