org.eigenbase.sql2rel
Class SqlToRelConverter.HistogramShuttle

java.lang.Object
  org.eigenbase.rex.RexShuttle
      org.eigenbase.sql2rel.SqlToRelConverter.HistogramShuttle

All Implemented Interfaces:

RexVisitor<RexNode>

Enclosing class:

SqlToRelConverter

private class SqlToRelConverter.HistogramShuttle
extends RexShuttle

Shuttle which walks over a tree of RexNodes and applies 'over' to all agg functions.

This is necessary because the returned expression is not necessarily a call to an agg function. For example,

AVG(x)

becomes

SUM(x) / COUNT(x)

Any aggregate functions are converted to calls to the internal $Histogram aggregation function and accessors such as $HistogramMin; for example,

MIN(x), MAX(x)

are converted to

$HistogramMin($Histogram(x)), $HistogramMax($Histogram(x))

Common sub-expression elmination will ensure that only one histogram is computed.

Field Summary

private RexNode[]	orderKeys
private RexNode[]	partitionKeys
private SqlWindow	window

Constructor Summary

SqlToRelConverter.HistogramShuttle(RexNode[] partitionKeys, RexNode[] orderKeys, SqlWindow window)

Method Summary

private RelDataType	computeHistogramType(RelDataType type) Returns the type for a histogram function.
(package private) SqlFunction	getHistogramOp(SqlAggFunction aggFunction) Returns the histogram operator corresponding to a given aggregate function.
RexNode	visitCall(RexCall call)

Methods inherited from class org.eigenbase.rex.RexShuttle

apply, apply, visitArray, visitCorrelVariable, visitDynamicParam, visitFieldAccess, visitInputRef, visitLiteral, visitLocalRef, visitOver, visitRangeRef, visitWindow

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

partitionKeys

private final RexNode[] partitionKeys

orderKeys

private final RexNode[] orderKeys

window

private final SqlWindow window

Constructor Detail

SqlToRelConverter.HistogramShuttle

SqlToRelConverter.HistogramShuttle(RexNode[] partitionKeys,
                                   RexNode[] orderKeys,
                                   SqlWindow window)

Method Detail

visitCall

public RexNode visitCall(RexCall call)

Specified by:

visitCall in interface RexVisitor<RexNode>

Overrides:

visitCall in class RexShuttle

getHistogramOp

SqlFunction getHistogramOp(SqlAggFunction aggFunction)

Returns the histogram operator corresponding to a given aggregate function.

For example, getHistogramOp(SqlStdOperatorTable.minOperator} returns SqlStdOperatorTable.histogramMinFunction.

Parameters:

aggFunction - An aggregate function

Returns:

Its histogram function, or null

computeHistogramType

private RelDataType computeHistogramType(RelDataType type)

Returns the type for a histogram function. It is either the actual type or an an approximation to it.