org.apache.druid.segment.join

Interface Joinable

All Superinterfaces:

ReferenceCountedObject

All Known Implementing Classes:

IndexedTableJoinable, LookupJoinable

public interface Joinable
extends ReferenceCountedObject

Represents something that can be the right-hand side of a join. This class's most important method is makeJoinMatcher(org.apache.druid.segment.ColumnSelectorFactory, org.apache.druid.segment.join.JoinConditionAnalysis, boolean). Its main user is HashJoinEngine.makeJoinCursor(org.apache.druid.segment.Cursor, org.apache.druid.segment.join.JoinableClause).

Field Summary

Fields

Modifier and Type	Field and Description
static int	CARDINALITY_UNKNOWN

Method Summary

Modifier and Type	Method and Description
List<String>	getAvailableColumns() Returns the list of columns that this Joinable offers.
int	getCardinality(String columnName) Returns the cardinality of "columnName", or CARDINALITY_UNKNOWN if not known.
ColumnCapabilities	getColumnCapabilities(String columnName) Returns capabilities for one of this Joinable's columns.
Optional<Set<String>>	getCorrelatedColumnValues(String searchColumnName, String searchColumnValue, String retrievalColumnName, long maxCorrelationSetSize, boolean allowNonKeyColumnSearch) Searches a column from this Joinable for a particular value, finds rows that match, and returns values of a second column for those rows.
JoinMatcher	makeJoinMatcher(ColumnSelectorFactory leftColumnSelectorFactory, JoinConditionAnalysis condition, boolean remainderNeeded) Creates a JoinMatcher that can be used to implement a join onto this Joinable.

Methods inherited from interface org.apache.druid.segment.ReferenceCountedObject

acquireReferences

Field Detail

CARDINALITY_UNKNOWN

static final int CARDINALITY_UNKNOWN

See Also:

Constant Field Values

Method Detail

getAvailableColumns

List<String> getAvailableColumns()

Returns the list of columns that this Joinable offers.

getCardinality

int getCardinality(String columnName)

Returns the cardinality of "columnName", or CARDINALITY_UNKNOWN if not known. May be used at query time to trigger optimizations. If not CARDINALITY_UNKNOWN, this must match the cardinality of selectors returned by the ColumnSelectorFactory.makeDimensionSelector(org.apache.druid.query.dimension.DimensionSpec) method of this joinable's JoinMatcher.getColumnSelectorFactory() .

getColumnCapabilities

@Nullable
ColumnCapabilities getColumnCapabilities(String columnName)

Returns capabilities for one of this Joinable's columns.

Parameters:

columnName - column name

Returns:

capabilities, or null if the columnName is not one of this Joinable's columns

makeJoinMatcher

JoinMatcher makeJoinMatcher(ColumnSelectorFactory leftColumnSelectorFactory,
                            JoinConditionAnalysis condition,
                            boolean remainderNeeded)

Creates a JoinMatcher that can be used to implement a join onto this Joinable.

Parameters:

leftColumnSelectorFactory - column selector factory that allows access to the left-hand side of the join

condition - join condition for the matcher

remainderNeeded - whether or not JoinMatcher.matchRemainder() will ever be called on the matcher. If we know it will not, additional optimizations are often possible.

Returns:

the matcher

getCorrelatedColumnValues

Optional<Set<String>> getCorrelatedColumnValues(String searchColumnName,
                                                String searchColumnValue,
                                                String retrievalColumnName,
                                                long maxCorrelationSetSize,
                                                boolean allowNonKeyColumnSearch)

Searches a column from this Joinable for a particular value, finds rows that match, and returns values of a second column for those rows.

Parameters:

searchColumnName - Name of the search column. This is the column that is being used in the filter

searchColumnValue - Target value of the search column. This is the value that is being filtered on.

retrievalColumnName - The column to retrieve values from. This is the column that is being joined against.

maxCorrelationSetSize - Maximum number of values to retrieve. If we detect that more values would be returned than this limit, return an empty set.

allowNonKeyColumnSearch - If true, allow searchs on non-key columns. If this is false, a search on a non-key column should return an empty set.

Returns:

The set of correlated column values. If we cannot determine correlated values, return absent. In case either the search or retrieval column names are not found, this will return absent.