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.
Signature
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.
Usage Examples
These examples are based on the .
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:
yearID
yearID
(the yearId 1986 is the only one in common)
By running the following query:
value
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.
select distinctCountThetaSketch(teamID) AS value
from baseballStats
select distinctCountThetaSketch(teamID, 'nominalEntries=10') AS value
from baseballStats
select yearID
from baseballStats
where teamID = 'SFN' AND numberOfGames = 28 AND homeRuns = 1
select yearID
from baseballStats
where teamID = 'CHN' AND numberOfGames = 28 AND homeRuns = 1
select distinctCountThetaSketch(
yearID,
'nominalEntries=4096',
'teamID = ''SFN'' AND numberOfGames=28 AND homeRuns=1',
'teamID = ''CHN'' AND numberOfGames=28 AND homeRuns=1',
'SET_INTERSECT($1, $2)'
) AS value
from baseballStats