AggregateExpression — Unevaluable Expression Container for AggregateFunction

AggregateExpression is an unevaluable expression (i.e. with no support for eval and doGenCode methods) that acts as a container for an AggregateFunction.

AggregateExpression contains the following:

AggregateFunction
AggregateMode
isDistinct flag indicating whether this aggregation is distinct or not (e.g. whether SQL’s DISTINCT keyword was used for the aggregate function)
ExprId

AggregateExpression is created when:

Analyzer resolves AggregateFunctions (and creates an AggregateExpression with Complete aggregate mode for the functions)
UserDefinedAggregateFunction is created with isDistinct flag disabled or enabled
AggUtils is requested to planAggregateWithOneDistinct (and creates AggregateExpressions with Partial and Final aggregate modes for the functions)
Aggregator is requested for a TypedColumn (using Aggregator.toColumn)
AggregateFunction is wrapped in a AggregateExpression

Table 1. toString’s Prefixes per AggregateMode
Prefix	AggregateMode
`partial_`	`Partial`
`merge_`	`PartialMerge`
(empty)	`Final` or `Complete`

Table 2. AggregateExpression’s Properties
Name	Description
`canonicalized`	AggregateExpression with AggregateFunction expression `canonicalized` with the special `ExprId` as `0`.
`children`	AggregateFunction expression (for which `AggregateExpression` was created).
`dataType`	DataType of AggregateFunction expression
`foldable`	Disabled (i.e. `false`)
`nullable`	Whether or not AggregateFunction expression is nullable.
`references`	`AttributeSet` with the following: `references` of AggregateFunction when AggregateMode is `Partial` or `Complete` aggBufferAttributes of AggregateFunction when `PartialMerge` or `Final`
`resultAttribute`	Attribute that is: `AttributeReference` when AggregateFunction is itself resolved `UnresolvedAttribute` otherwise
`sql`	Requests AggregateFunction to generate SQL output (with isDistinct flag).
`toString`	Prefix per AggregateMode followed by AggregateFunction's `toAggString` (with isDistinct flag).

AggregateExpression

AggregateExpression — Unevaluable Expression Container for AggregateFunction

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