org.apache.derby.iapi.sql.compile

Interface OptimizablePredicate

All Known Implementing Classes:

Predicate

public interface OptimizablePredicate

OptimizablePredicate provides services for optimizing predicates in a query.

Method Summary

Modifier and Type	Method and Description
boolean	compareWithKnownConstant(Optimizable optTable, boolean considerParameters) Is this predicate a comparison with a known constant value?
boolean	equalsComparisonWithConstantExpression(Optimizable optTable) Is this predicate an equality comparison with a constant expression? (IS NULL is considered to be an = comparison with a constant expression).
DataValueDescriptor	getCompareValue(Optimizable optTable) Get an Object representing the known constant value that the given Optimizable is being compared to.
int	getIndexPosition() Get the position of the index column that this predicate restricts.
JBitSet	getReferencedMap() Get the map of referenced tables for this OptimizablePredicate.
int	hasEqualOnColumnList(int[] baseColumnPositions, Optimizable optTable) Returns if the predicate involves an equal operator on one of the columns specified in the baseColumnPositions.
boolean	hasMethodCall() Return whether or not an OptimizablePredicate contains a method call.
boolean	hasSubquery() Return whether or not an OptimizablePredicate contains a subquery.
boolean	isQualifier() Is this predicate a qualifier?
boolean	isStartKey() Is this predicate a start key?
boolean	isStopKey() Is this predicate a stop key?
void	markQualifier() Tell the predicate that it is to be used as a qualifier in an index scan.
void	markStartKey() Tell the predicate that it is to be used as a column in the start key value for an index scan.
void	markStopKey() Tell the predicate that it is to be used as a column in the stop key value for an index scan.
double	selectivity(Optimizable optTable) Get a (crude) estimate of the selectivity of this predicate.

Method Detail

getReferencedMap

JBitSet getReferencedMap()

Get the map of referenced tables for this OptimizablePredicate.

Returns:

JBitSet Referenced table map.

hasSubquery

boolean hasSubquery()

Return whether or not an OptimizablePredicate contains a subquery.

Returns:

boolean Whether or not an OptimizablePredicate includes a subquery.

hasMethodCall

boolean hasMethodCall()

Return whether or not an OptimizablePredicate contains a method call.

Returns:

boolean Whether or not an OptimizablePredicate includes a method call.

markStartKey

void markStartKey()

Tell the predicate that it is to be used as a column in the start key value for an index scan.

isStartKey

boolean isStartKey()

Is this predicate a start key?

markStopKey

void markStopKey()

Tell the predicate that it is to be used as a column in the stop key value for an index scan.

isStopKey

boolean isStopKey()

Is this predicate a stop key?

markQualifier

void markQualifier()

Tell the predicate that it is to be used as a qualifier in an index scan.

isQualifier

boolean isQualifier()

Is this predicate a qualifier?

compareWithKnownConstant

boolean compareWithKnownConstant(Optimizable optTable,
                                 boolean considerParameters)

Is this predicate a comparison with a known constant value?

Parameters:

optTable - The Optimizable that we want to know whether we are comparing to a known constant.

considerParameters - Whether or not to consider parameters with defaults as known constants.

getCompareValue

DataValueDescriptor getCompareValue(Optimizable optTable)
                             throws StandardException

Get an Object representing the known constant value that the given Optimizable is being compared to.

Throws:

StandardException - Thrown on error

equalsComparisonWithConstantExpression

boolean equalsComparisonWithConstantExpression(Optimizable optTable)

Is this predicate an equality comparison with a constant expression? (IS NULL is considered to be an = comparison with a constant expression).

Parameters:

optTable - The Optimizable for which we want to know whether it is being equality-compared to a constant expression.

hasEqualOnColumnList

int hasEqualOnColumnList(int[] baseColumnPositions,
                         Optimizable optTable)
                  throws StandardException

Returns if the predicate involves an equal operator on one of the columns specified in the baseColumnPositions.

Parameters:

baseColumnPositions - the column numbers on which the user wants to check if the equality condition exists.

optTable - the table for which baseColumnPositions are given.

Returns:

returns the index into baseColumnPositions of the column that has the equality operator.

Throws:

StandardException

selectivity

double selectivity(Optimizable optTable)
            throws StandardException

Get a (crude) estimate of the selectivity of this predicate. This is to be used when no better technique is available for estimating the selectivity - this method's estimate is a hard- wired number based on the type of predicate and the datatype (the selectivity of boolean is always 50%).

Parameters:

optTable - The Optimizable that this predicate restricts

Throws:

StandardException

getIndexPosition

int getIndexPosition()

Get the position of the index column that this predicate restricts. NOTE: This assumes that this predicate is part of an OptimizablePredicateList, and that classify() has been called on the OptimizablePredicateList.

Returns:

The index position that this predicate restricts (zero-based)