[doc] Add exponential_moving_average aggregate function documentation#3726
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### What problem does this PR solve? Problem Summary: Doris added the exponential_moving_average aggregate function but no documentation existed. - English doc with syntax, parameters, return value, and examples (basic, GROUP BY, NULL handling, empty set, window function, constant requirement). - Chinese (zh-CN) translation. - Sidebar entry in both aggregate-functions and analytic-functions lists. ### Release note None ### Check List (For Author) - Test: No need to test (docs only) - Behavior changed: No - Does this need documentation: No (this IS the documentation)
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HappenLee
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…63499) Problem Summary: Doris lacked an exponential moving average aggregate function. This implements `exponential_moving_average(half_decay, value, time)` ported from ClickHouse's ExponentialMovingAverage aggregate. Algorithm: - State stores (value, time, half_decay) as doubles. - On add(): scale existing value to the new timestamp via `2^(-dt/half_decay)`, then accumulate. Store half_decay in state so it is available during merge(). - On merge(): advance both states to the later timestamp, then sum. This is commutative and associative, so row order doesn't matter. - Result: `value * (1 - 2^(-1/half_decay))` (normalised by sum of weights). Changes: - BE: `aggregate_function_ema.h/cpp` — state struct + function class, registered in `aggregate_function_simple_factory.cpp`. - FE: `ExponentialMovingAverage.java` — 3-arg DOUBLE signature, visitor method added to `AggregateFunctionVisitor`, registered in `BuiltinAggregateFunctions`. - Regression test: `query_p0/aggregate/exponential_moving_average/`. ### Release note New aggregate function `exponential_moving_average(half_decay, value, time)` computes the exponential moving average over a stream of (value, time) pairs with the given half-decay parameter. ### Check List (For Author) - Test: Regression test added (query_p0/aggregate/exponential_moving_average) - Behavior changed: No (new function) - Does this need documentation: [docs](apache/doris-website#3726) --------- Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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What problem does this PR solve?
Problem Summary:
Doris added the exponential_moving_average aggregate function but no documentation existed.
Release note
None
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