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fix: ignore ordering in approx_median #27159

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fix: ignore ordering in approx_median #27159

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6 changes: 5 additions & 1 deletion datafusion/functions-aggregate/src/approx_median.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -13,7 +13,7 @@ use std::sync::Arc;

use datafusion_common::{Result, not_impl_err};
use datafusion_expr::function::{AccumulatorArgs, StateFieldsArgs};
use datafusion_expr::utils::format_state_name;
use datafusion_expr::utils::{AggregateOrderSensitivity, format_state_name};
use datafusion_expr::{
Accumulator, AggregateUDFImpl, Coercion, Documentation, Signature, TypeSignature,
TypeSignatureClass, Volatility,
Expand Down Expand Up @@ -137,6 +137,10 @@ impl AggregateUDFImpl for ApproxMedian {
}
}

fn order_sensitivity(&self) -> AggregateOrderSensitivity {
AggregateOrderSensitivity::Insensitive
}

fn documentation(&self) -> Option<&Documentation> {
self.doc()
}
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8 changes: 8 additions & 0 deletions datafusion/sqllogictest/test_files/aggregate.slt
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Expand Up @@ -759,6 +759,14 @@ SELECT approx_median(c12) FROM aggregate_test_100
statement error
SELECT approx_median(c1) FROM aggregate_test_100

# APPROX_MEDIAN ignores aggregate ORDER BY keys. They must not be interpreted

@alamb alamb Nov 8, 2026

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Does it make sense to support ORDER BY that is just ignored?
What do other systems (postgres?) do?

I think it would be better to reject this query with a more specific message

# as percentile arguments by the shared accumulator.
query R
SELECT approx_median(x ORDER BY k)
FROM (VALUES (1.0, 3), (2.0, 1), (3.0, 2)) t(x, k)
----
2

# csv_query_median_1
query R
SELECT median(c2) FROM aggregate_test_100
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