org.apache.calcite.sql2rel

Class SqlToRelConverter.HistogramShuttle

java.lang.Object

org.apache.calcite.rex.RexShuttle

org.apache.calcite.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 elimination will ensure that only one histogram is computed.

Field Summary

Fields

Modifier and Type	Field and Description
private boolean	distinct
(package private) static boolean	ENABLE_HISTOGRAM_AGG Whether to convert calls to MIN(x) to HISTOGRAM_MIN(HISTOGRAM(x)).
private RexWindowBound	lowerBound
private com.google.common.collect.ImmutableList<RexFieldCollation>	orderKeys
private List<RexNode>	partitionKeys
private RexWindowBound	upperBound
private SqlWindow	window

Constructor Summary

Constructors

Constructor and Description
HistogramShuttle(List<RexNode> partitionKeys, com.google.common.collect.ImmutableList<RexFieldCollation> orderKeys, RexWindowBound lowerBound, RexWindowBound upperBound, SqlWindow window, boolean distinct)

Method Summary

Modifier and Type	Method and Description
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.apache.calcite.rex.RexShuttle

apply, apply, apply, mutate, visitArray, visitCorrelVariable, visitDynamicParam, visitFieldAccess, visitFieldCollations, visitInputRef, visitList, visitList, visitLiteral, visitLocalRef, visitOver, visitPatternFieldRef, visitRangeRef, visitSubQuery, visitTableInputRef, visitWindow

Methods inherited from class java.lang.Object

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

Field Detail

ENABLE_HISTOGRAM_AGG

static final boolean ENABLE_HISTOGRAM_AGG

Whether to convert calls to MIN(x) to HISTOGRAM_MIN(HISTOGRAM(x)). Histograms allow rolling computation, but require more space.

See Also:

Constant Field Values

partitionKeys

private final List<RexNode> partitionKeys

orderKeys

private final com.google.common.collect.ImmutableList<RexFieldCollation> orderKeys

lowerBound

private final RexWindowBound lowerBound

upperBound

private final RexWindowBound upperBound

window

private final SqlWindow window

distinct

private final boolean distinct

Constructor Detail

HistogramShuttle

HistogramShuttle(List<RexNode> partitionKeys,
                 com.google.common.collect.ImmutableList<RexFieldCollation> orderKeys,
                 RexWindowBound lowerBound,
                 RexWindowBound upperBound,
                 SqlWindow window,
                 boolean distinct)

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.MIN} returns SqlStdOperatorTable.HISTOGRAM_MIN.

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.