AggregateExpression — Unevaluable Expression Container for AggregateFunction¶

AggregateExpression is an unevaluable expression that acts as a container for an AggregateFunction.

AggregateExpression contains the following:

• [[aggregateFunction]] AggregateFunction
• [[mode]] AggregateMode
• [[isDistinct]] isDistinct flag indicating whether this aggregation is distinct or not (e.g. whether SQL's DISTINCT keyword was used for the <>)
• [[resultId]] ExprId

AggregateExpression is created when:

• Analyzer is requested to resolve 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 spark-sql-TypedColumn.md[TypedColumn] (using Aggregator.toColumn)

• AggregateFunction is spark-sql-Expression-AggregateFunction.md#toAggregateExpression[wrapped in a AggregateExpression]

[[toString-prefixes]] .toString's Prefixes per AggregateMode [cols="1,2",options="header",width="100%"] |=== | Prefix | AggregateMode

| partial_ | Partial

| merge_ | PartialMerge

| (empty) | Final or Complete |===

[[properties]] .AggregateExpression's Properties [width="100%",cols="1,2",options="header"] |=== | Name | Description

| canonicalized | AggregateExpression with <> expression canonicalized with the special ExprId as 0.

| children | <> expression (for which AggregateExpression was created).

| dataType | DataType of AggregateFunction expression

| foldable | Disabled (i.e. false)

| nullable | Whether or not <> expression is nullable.

| [[references]] references a| AttributeSet with the following:

• references of <> when <> is Partial or Complete

• spark-sql-Expression-AggregateFunction.md#aggBufferAttributes[aggBufferAttributes] of <> when PartialMerge or Final

| resultAttribute a|

spark-sql-Expression-Attribute.md[Attribute] that is:

• AttributeReference when <> is itself resolved

• UnresolvedAttribute otherwise

| sql | Requests <> to generate SQL output (with <> flag).

| toString | <> followed by <>'s toAggString (with <> flag). |===