This section contains reference documentation for the DISTINCTCOUNTTHETASKETCH function.
The Theta Sketch framework enables set operations over a stream of data, and can also be used for cardinality estimation. Pinot leverages the Sketch Class and its extensions from the library org.apache.datasketches:datasketches-java:4.2.0
to perform distinct counting as well as evaluating set operations.
distinctCountThetaSketch(<thetaSketchColumn>, <thetaSketchParams>, predicate1, predicate2..., postAggregationExpressionToEvaluate) -> Long
thetaSketchColumn
(required): Name of the column to aggregate on.
thetaSketchParams
(required): Parameters for constructing the intermediate theta-sketches.
Currently, the only supported parameter is nominalEntries
(defaults to 4096).
predicates
(optional)_: _ These are individual predicates of form lhs <op> rhs
which are applied on rows selected by the where
clause. During intermediate sketch aggregation, sketches from the thetaSketchColumn
that satisfies these predicates are unionized individually. For example, all filtered rows that match country=USA
are unionized into a single sketch. Complex predicates that are created by combining (AND/OR) of individual predicates is supported.
postAggregationExpressionToEvaluate
(required): The set operation to perform on the individual intermediate sketches for each of the predicates. Currently supported operations are SET_DIFF, SET_UNION, SET_INTERSECT
, where DIFF requires two arguments and the UNION/INTERSECT allow more than two arguments.
These examples are based on the Batch Quick Start.
value |
---|
value |
---|
We can also provide predicates and a post aggregation expression to compute more complicated cardinalities. For example, we could can find the intersection of the following queries:
(the yearId 1986
is the only one in common)
By running the following query:
yearID |
---|
yearID |
---|
value |
---|
149
146
1986
1985
1937
2003
1979
1900
1986
1978
2012
1