spark技术分享DeclarativeAggregate Contract — Unevaluable Aggregate Function Expressions
DeclarativeAggregate is an extension of the AggregateFunction Contract for aggregate function expressions that are unevaluable and use expressions for evaluation.
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An unevaluable expression cannot be evaluated to produce a value (neither in interpreted nor code-generated expression evaluations) and has to be resolved (replaced) to some other expressions or logical operators at analysis or optimization phases or they fail analysis. |
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The expression that returns the final value for the aggregate function Used when:
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