com.facebook.presto.sql.planner.iterative.properties

Class Key

java.lang.Object

com.facebook.presto.sql.planner.iterative.properties.Key

public class Key
extends Object

Represents a primary or unique key constraint that holds for a final or intermediate result set produced by a PlanNode. It can also be used to represent a key requirement that must be satisfied by a PlanNode (e.g. distinct requirement)

Constructor Summary

Constructors

Constructor and Description
Key(Set<VariableReferenceExpression> variables) A set of variable references that satisfy a primary or unique key constraint.

Method Summary

Modifier and Type	Method and Description
Key	concat(Key toConcatKey) Returns a version of this key concatenated with the provided key.
boolean	keySatisifiesRequirement(Key keyRequirement) Determines if a provided key requirement is satisfied by this key.
Optional<Key>	normalize(EquivalenceClassProperty equivalenceClassProperty) Returns a canonical version of this key wherein duplicate or constant variables are removed and any remaining variables are replaced with their equivalence class heads.
Optional<Key>	project(LogicalPropertiesImpl.InverseVariableMappingsWithEquivalence inverseVariableMappings) Returns a projected version of this key.
String	toString()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

Key

public Key(Set<VariableReferenceExpression> variables)

A set of variable references that satisfy a primary or unique key constraint.

Parameters:

variables -

Method Detail

keySatisifiesRequirement

public boolean keySatisifiesRequirement(Key keyRequirement)

Determines if a provided key requirement is satisfied by this key. This is true if the variables in this key are a subset of the variables in the key requirement. Note the this operation should be called only after using the normalize method to render the key and key requirement into their canonical forms using equivalence classes.

Parameters:

keyRequirement -

Returns:

True if this key satisfies the key requirement and False otherwise.

normalize

public Optional<Key> normalize(EquivalenceClassProperty equivalenceClassProperty)

Returns a canonical version of this key wherein duplicate or constant variables are removed and any remaining variables are replaced with their equivalence class heads. Note that if all key variables are bound to constants an empty result is returned, signaling that at most a single record is in the result set constrained by this key.

Parameters:

equivalenceClassProperty -

Returns:

A normalized version of this key or empty if all variables are bound to constants.

project

public Optional<Key> project(LogicalPropertiesImpl.InverseVariableMappingsWithEquivalence inverseVariableMappings)

Returns a projected version of this key. Variables in the key are mapped to output variables in the context beyond the project operation. If a key attribute does not have an assignment in the new attribute context, it is mapped to the assignment of an equivalent attribute whenever possible. For example, assume A is a key attribute and there is no new assignment for A. Assume further that A and B are in the same equivalence class and there is an assignment from B to B’. Consequently, A can be assigned to B' rather than get projected. If any of the variables are not mapped then an empty result is returned signaling that the key is effectively uninteresting beyond the project operation and hence is not propagated.

Parameters:

inverseVariableMappings -

Returns:

A projected version of this key or empty if any variables are not propagated.

concat

public Key concat(Key toConcatKey)

Returns a version of this key concatenated with the provided key. A concatenated key results from a join operation where concatenated keys of the left and right join inputs form unique constraints on the join result.

Parameters:

toConcatKey -

Returns:

a version of this key concatenated with the provided key.

toString

public String toString()

Overrides:

toString in class Object