org.apache.druid.segment.join

Interface JoinMatcher

All Known Implementing Classes:

IndexedTableJoinMatcher, LookupJoinMatcher

public interface JoinMatcher

An interface returned by Joinable.makeJoinMatcher(org.apache.druid.segment.ColumnSelectorFactory, org.apache.druid.segment.join.JoinConditionAnalysis, boolean) and used by HashJoinEngine to implement a join. A typical usage would go something like:

 matcher.matchCondition();
 while (matcher.hasMatch()) {
   // Do something with the match
   matcher.nextMatch();
 }
 

Method Summary

Modifier and Type	Method and Description
ColumnSelectorFactory	getColumnSelectorFactory() Returns a factory for reading columns from the Joinable that correspond to matched rows.
boolean	hasMatch() Returns whether the active matcher (matchCondition() or matchRemainder()) has matched something.
void	matchCondition() Matches against the ColumnSelectorFactory and JoinConditionAnalysis supplied to Joinable.makeJoinMatcher(org.apache.druid.segment.ColumnSelectorFactory, org.apache.druid.segment.join.JoinConditionAnalysis, boolean).
boolean	matchingRemainder() Returns whether this matcher is currently matching the remainder (i.e.
void	matchRemainder() Matches every row that has not already been matched.
void	nextMatch() Moves on to the next match.
void	reset() Clears any active matches.

Method Detail

getColumnSelectorFactory

ColumnSelectorFactory getColumnSelectorFactory()

Returns a factory for reading columns from the Joinable that correspond to matched rows.

matchCondition

void matchCondition()

Matches against the ColumnSelectorFactory and JoinConditionAnalysis supplied to Joinable.makeJoinMatcher(org.apache.druid.segment.ColumnSelectorFactory, org.apache.druid.segment.join.JoinConditionAnalysis, boolean). After calling this method, hasMatch() will return whether at least one row matched. After reading that row, nextMatch() can be used to move on to the next row.

matchRemainder

void matchRemainder()

Matches every row that has not already been matched. Used for right joins. After calling this method, hasMatch() will return whether at least one row matched. After reading that row, nextMatch() can be used to move on to the next row. Will only work correctly if Joinable.makeJoinMatcher(org.apache.druid.segment.ColumnSelectorFactory, org.apache.druid.segment.join.JoinConditionAnalysis, boolean) was called with remainderNeeded == true.

hasMatch

boolean hasMatch()

Returns whether the active matcher (matchCondition() or matchRemainder()) has matched something.

nextMatch

void nextMatch()

Moves on to the next match. It is only valid to call this if hasMatch() is true.

matchingRemainder

boolean matchingRemainder()

Returns whether this matcher is currently matching the remainder (i.e. if matchRemainder() was the most recent match method called).

reset

void reset()

Clears any active matches. Does not clear memory about what has been matched in the past.