Package org.apache.druid.query

Class JoinDataSource

java.lang.Object
org.apache.druid.query.JoinDataSource
All Implemented Interfaces:
Cacheable, DataSource
public class JoinDataSource extends Object implements DataSource
Represents a join of two datasources.

Logically, this datasource contains the result of:

(1) prefixing all right-side columns with "rightPrefix" (2) then, joining the left and (prefixed) right sides using the provided type and condition

Any columns from the left-hand side that start with "rightPrefix", and are at least one character longer than the prefix, will be shadowed. It is up to the caller to ensure that no important columns are shadowed by the chosen prefix.

When analyzed by JoinDataSourceAnalysis, the right-hand side of this datasource will become a PreJoinableClause object.

  • Method Details

    • create

      public static JoinDataSource create(DataSource left, DataSource right, String rightPrefix, String condition, JoinType joinType, @Nullable DimFilter leftFilter, ExprMacroTable macroTable, @Nullable JoinableFactoryWrapper joinableFactoryWrapper, @Nullable JoinAlgorithm joinAlgorithm)
      Create a join dataSource from a string condition.

    • create

      public static JoinDataSource create(DataSource left, DataSource right, String rightPrefix, JoinConditionAnalysis conditionAnalysis, JoinType joinType, DimFilter leftFilter, @Nullable JoinableFactoryWrapper joinableFactoryWrapper, @Nullable JoinAlgorithm joinAlgorithm)
      Create a join dataSource from an existing JoinConditionAnalysis.

    • getTableNames

      public Set<String> getTableNames()
      Description copied from interface: DataSource
      Returns the names of all table datasources involved in this query. Does not include names for non-tables, like lookups or inline datasources.
      Specified by:
      getTableNames in interface DataSource

    • getLeft

      public DataSource getLeft()

    • getRight

      public DataSource getRight()

    • getRightPrefix

      public String getRightPrefix()

    • getCondition

      public String getCondition()

    • getConditionAnalysis

      public JoinConditionAnalysis getConditionAnalysis()

    • getJoinType

      public JoinType getJoinType()

    • getLeftFilter

      @Nullable public DimFilter getLeftFilter()

    • getJoinableFactoryWrapper

      @Nullable public JoinableFactoryWrapper getJoinableFactoryWrapper()

    • getChildren

      public List<DataSource> getChildren()
      Description copied from interface: DataSource
      Returns datasources that this datasource depends on. Will be empty for leaf datasources like 'table'.
      Specified by:
      getChildren in interface DataSource

    • withChildren

      public DataSource withChildren(List<DataSource> children)
      Description copied from interface: DataSource
      Return a new DataSource, identical to this one, with different children. The number of children must be equal to the number of children that this datasource already has.
      Specified by:
      withChildren in interface DataSource

    • isCacheable

      public boolean isCacheable(boolean isBroker)
      Description copied from interface: DataSource
      Returns true if queries on this dataSource are cacheable at both the result level and per-segment level. Currently, dataSources that do not actually reference segments (like 'inline'), are not cacheable since cache keys are always based on segment identifiers.
      Specified by:
      isCacheable in interface DataSource

    • isGlobal

      public boolean isGlobal()
      Description copied from interface: DataSource
      Decides if this datasource can be accessed globally.

      This means that all servers have a full copy of this datasource.

      Examples: inline table, lookup.

      Specified by:
      isGlobal in interface DataSource

    • isProcessable

      public boolean isProcessable()
      Description copied from interface: DataSource
      Communicates that this DataSource can be directly used to run a Query.

      A Processable datasource must pack the necessary logic into the DataSource.createSegmentMapFunction(Query).

      Processable examples are: TableDataSource, InlineDataSource, FilteredDataSource. Non-processable ones are those which need further pre-processing before running them. examples are: QueryDataSource and join which are not supported directly.

      Specified by:
      isProcessable in interface DataSource

    • getVirtualColumnCandidates

      public Set<String> getVirtualColumnCandidates()
      Computes a set of column names for left table expressions in join condition which may already have been defined as a virtual column in the virtual column registry. It helps to remove any extraenous virtual columns created and only use the relevant ones.
      Returns:
      a set of column names which might be virtual columns on left table in join condition

    • getCacheKey

      public byte[] getCacheKey()
      Description copied from interface: DataSource
      Compute a cache key prefix for a data source. This includes the data sources that participate in the RHS of a join as well as any query specific constructs associated with join data source such as base table filter. This key prefix can be used in segment level cache or result level cache. The function can return following - Non-empty byte array - If there is join datasource involved and caching is possible. The result includes join condition expression, join type and cache key returned by joinable factory for each PreJoinableClause - NULL - There is a join but caching is not possible. It may happen if one of the participating datasource in the JOIN is not cacheable.
      Specified by:
      getCacheKey in interface Cacheable
      Specified by:
      getCacheKey in interface DataSource
      Returns:
      the cache key to be used as part of query cache key

    • getJoinAlgorithm

      public JoinAlgorithm getJoinAlgorithm()

    • equals

      public boolean equals(Object o)
      Overrides:
      equals in class Object

    • hashCode

      public int hashCode()
      Overrides:
      hashCode in class Object

    • toString

      public String toString()
      Overrides:
      toString in class Object

    • createSegmentMapFunction

      public SegmentMapFunction createSegmentMapFunction(Query query)
      Creates a Function that maps base segments to HashJoinSegment if needed (i.e. if the number of join clauses is > 0). If mapping is not needed, this method will return Function.identity().
      Specified by:
      createSegmentMapFunction in interface DataSource
      Parameters:
      query -

    • createSegmentMapFunction

      public static SegmentMapFunction createSegmentMapFunction(List<JoinableClause> clausesToUse, Filter baseFilterToUse, JoinFilterPreAnalysis joinFilterPreAnalysis, SegmentMapFunction baseMapFn)

    • getJoinAnalysisForDataSource

      public JoinDataSourceAnalysis getJoinAnalysisForDataSource()
      Computes the DataSourceAnalysis with join boundaries. It will only process what the join datasource could handle in one go - and not more.