LastValue

LastValue is a term used in programming and data processing to denote the most recently observed value in a sequence, stream, or dataset. It can refer to a general concept of retaining the latest value, or to a specific function or operator named lastValue in a language or library. In practice, lastValue is often used in streaming analytics, dashboards, and windowed queries where the latest data point is required for comparisons, aggregation, or stateful processing. Implementations must consider initial values, nulls, and late-arriving data.

In SQL, the LAST_VALUE analytic function returns the value of an expression for the current row within its window. Its result depends on the defined window frame, and to obtain the true last value across a partition you typically specify a frame such as ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW. Different SQL dialects may provide variations or additional options for handling nulls and frame boundaries.

In functional and reactive programming, several libraries expose concepts or operators that yield the last value of a stream or sequence. Depending on the platform, this may be implemented as a dedicated lastValue operator or as a combination of existing operators like last, reduce, or fold. Some ecosystems also provide a convenience function to obtain the last emitted value from a stream, sometimes converting it into a single future or promise.

In time-series databases and metrics platforms, lastValue commonly denotes the most recent data point for a given series, and is frequently used in dashboards, alerts, and trend analyses. See also: last, LAST_VALUE, window function.