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, boolean, org.apache.druid.java.util.common.io.Closer). Its main user is HashJoinEngine.makeJoinCursor(org.apache.druid.segment.Cursor, org.apache.druid.segment.join.JoinableClause, boolean, org.apache.druid.java.util.common.io.Closer).

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static class	Joinable.ColumnValuesWithUniqueFlag

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.
Joinable.ColumnValuesWithUniqueFlag	getNonNullColumnValues(String columnName, int maxNumValues) Returns all non-null values from a particular column along with a flag to tell if they are all unique in the column.
JoinMatcher	makeJoinMatcher(ColumnSelectorFactory leftColumnSelectorFactory, JoinConditionAnalysis condition, boolean remainderNeeded, boolean descending, Closer closer) 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,
                            boolean descending,
                            Closer closer)

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.

descending - true if join cursor is iterated in descending order

closer - closer that will run after join cursor has completed to clean up any per query resources the joinable uses

Returns:

the matcher

getNonNullColumnValues

Joinable.ColumnValuesWithUniqueFlag getNonNullColumnValues(String columnName,
                                                           int maxNumValues)

Returns all non-null values from a particular column along with a flag to tell if they are all unique in the column. If the non-null values are greater than "maxNumValues" or if the column doesn't exists or doesn't supports this operation, returns an object with empty set for column values and false for uniqueness flag. The uniqueness flag will only be true if we've collected all non-null values in the column and found that they're all unique. In all other cases it will be false. The returned set may be passed to InDimFilter. For efficiency, implementations should prefer creating the returned set with new TreeSet<String>(Comparators.naturalNullsFirst()}. This avoids a copy in the filter's constructor.

Parameters:

columnName - name of the column

maxNumValues - maximum number of values to return

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. The returned set may be passed to InDimFilter. For efficiency, implementations should prefer creating the returned set with new TreeSet<String>(Comparators.naturalNullsFirst()}. This avoids a copy in the filter's constructor.

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 absent.

allowNonKeyColumnSearch - If true, allow searchs on non-key columns. If this is false, a search on a non-key column returns absent.

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.