org.h2.expression
Class Expression

java.lang.Object
  extended by org.h2.expression.Expression
Direct Known Subclasses:
Aggregate, Alias, Condition, 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
Expression()
           
 
Method Summary
 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.
 java.lang.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 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 values.
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 isEverything(int expressionVisitorType)
          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.
 Expression optimizeInJoin(Session session, Select select)
          Optimize IN(...) expressions if possible.
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)
                        throws java.sql.SQLException
Return the resulting value for the current row.

Parameters:
session - the session
Returns:
the result
Throws:
java.sql.SQLException

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)
                         throws java.sql.SQLException
Map the columns of the resolver to expression columns.

Parameters:
resolver - the column resolver
level - the subquery nesting level
Throws:
java.sql.SQLException

optimize

public abstract Expression optimize(Session session)
                             throws java.sql.SQLException
Try to optimize the expression.

Parameters:
session - the session
Returns:
the optimized expression
Throws:
java.sql.SQLException

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)
                              throws java.sql.SQLException
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
Throws:
java.sql.SQLException

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

isEverything

public final boolean isEverything(int expressionVisitorType)
Check if this expression and all sub-expressions can fulfill a criteria. This is a convenience function.

Parameters:
expressionVisitorType - the visitor type
Returns:
if the criteria can be fulfilled

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:
if it is set

isAutoIncrement

public boolean isAutoIncrement()
Check if this is an auto-increment column.

Returns:
true if it is an auto-increment column

getBooleanValue

public java.lang.Boolean getBooleanValue(Session session)
                                  throws java.sql.SQLException
Get the value in form of a boolean expression. Returns true, false, or null. In this database, everything can be a condition.

Parameters:
session - the session
Returns:
the result
Throws:
java.sql.SQLException

createIndexConditions

public void createIndexConditions(Session session,
                                  TableFilter filter)
                           throws java.sql.SQLException
Create index conditions if possible and attach them to the table filter.

Parameters:
session - the session
filter - the table filter
Throws:
java.sql.SQLException

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 values.

Returns:
whether null values are 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

optimizeInJoin

public Expression optimizeInJoin(Session session,
                                 Select select)
                          throws java.sql.SQLException
Optimize IN(...) expressions if possible.

Parameters:
session - the session
select - the query
Returns:
the optimized expression
Throws:
java.sql.SQLException