duckdb · hannes · Jan 21, 2026 · Jan 23, 2026 · Feb 2, 2026 · Feb 3, 2026
diff --git a/CMakeLists.txt b/CMakeLists.txt
diff --git a/src/duckdb/extension/core_functions/aggregate/algebraic/avg.cpp b/src/duckdb/extension/core_functions/aggregate/algebraic/avg.cpp
@@ -239,27 +239,47 @@ struct TimeTZAverageOperation : public BaseSumOperation<AverageSetOperation, Add
 	}
 };
 
+LogicalType GetAvgStateType(const AggregateFunction &function) {
+	child_list_t<LogicalType> children;
+	children.emplace_back("count", LogicalType::UBIGINT);
+	children.emplace_back("value", function.arguments[0]);
+	return LogicalType::STRUCT(std::move(children));
+}
+
+LogicalType GetKahanAvgStateType(const AggregateFunction &function) {
+	child_list_t<LogicalType> children;
+	children.emplace_back("count", LogicalType::UBIGINT);
+	children.emplace_back("value", LogicalType::DOUBLE);
+	children.emplace_back("err", LogicalType::DOUBLE);
+	return LogicalType::STRUCT(std::move(children));
+}
+
 AggregateFunction GetAverageAggregate(PhysicalType type) {
 	switch (type) {
 	case PhysicalType::INT16: {
 		return AggregateFunction::UnaryAggregate<AvgState<int64_t>, int16_t, double, IntegerAverageOperation>(
-		    LogicalType::SMALLINT, LogicalType::DOUBLE);
+		           LogicalType::SMALLINT, LogicalType::DOUBLE)
+		    .SetStructStateExport(GetAvgStateType);
 	}
 	case PhysicalType::INT32: {
 		return AggregateFunction::UnaryAggregate<AvgState<hugeint_t>, int32_t, double, IntegerAverageOperationHugeint>(
-		    LogicalType::INTEGER, LogicalType::DOUBLE);
+		           LogicalType::INTEGER, LogicalType::DOUBLE)
+		    .SetStructStateExport(GetAvgStateType);
 	}
 	case PhysicalType::INT64: {
 		return AggregateFunction::UnaryAggregate<AvgState<hugeint_t>, int64_t, double, IntegerAverageOperationHugeint>(
-		    LogicalType::BIGINT, LogicalType::DOUBLE);
+		           LogicalType::BIGINT, LogicalType::DOUBLE)
+		    .SetStructStateExport(GetAvgStateType);
 	}
 	case PhysicalType::INT128: {
 		return AggregateFunction::UnaryAggregate<AvgState<hugeint_t>, hugeint_t, double, HugeintAverageOperation>(
-		    LogicalType::HUGEINT, LogicalType::DOUBLE);
+		           LogicalType::HUGEINT, LogicalType::DOUBLE)
+		    .SetStructStateExport(GetAvgStateType);
 	}
 	case PhysicalType::INTERVAL: {
 		return AggregateFunction::UnaryAggregate<IntervalAvgState, interval_t, interval_t, IntervalAverageOperation>(
-		    LogicalType::INTERVAL, LogicalType::INTERVAL);
+		           LogicalType::INTERVAL, LogicalType::INTERVAL)
+		    .SetStructStateExport(GetAvgStateType);
 	}
 	default:
 		throw InternalException("Unimplemented average aggregate");
@@ -282,6 +302,7 @@ unique_ptr<FunctionData> BindDecimalAvg(ClientContext &context, AggregateFunctio
 AggregateFunctionSet AvgFun::GetFunctions() {
 	AggregateFunctionSet avg;
 
+	// The first is already opted-in during `BindDecimalAvg`
 	avg.AddFunction(AggregateFunction({LogicalTypeId::DECIMAL}, LogicalTypeId::DECIMAL, nullptr, nullptr, nullptr,
 	                                  nullptr, nullptr, FunctionNullHandling::DEFAULT_NULL_HANDLING, nullptr,
 	                                  BindDecimalAvg));
@@ -291,24 +312,31 @@ AggregateFunctionSet AvgFun::GetFunctions() {
 	avg.AddFunction(GetAverageAggregate(PhysicalType::INT128));
 	avg.AddFunction(GetAverageAggregate(PhysicalType::INTERVAL));
 	avg.AddFunction(AggregateFunction::UnaryAggregate<AvgState<double>, double, double, NumericAverageOperation>(
-	    LogicalType::DOUBLE, LogicalType::DOUBLE));
+	                    LogicalType::DOUBLE, LogicalType::DOUBLE)
+	                    .SetStructStateExport(GetAvgStateType));
 
 	avg.AddFunction(AggregateFunction::UnaryAggregate<AvgState<hugeint_t>, int64_t, int64_t, DiscreteAverageOperation>(
-	    LogicalType::TIMESTAMP, LogicalType::TIMESTAMP));
+	                    LogicalType::TIMESTAMP, LogicalType::TIMESTAMP)
+	                    .SetStructStateExport(GetAvgStateType));
 	avg.AddFunction(AggregateFunction::UnaryAggregate<AvgState<hugeint_t>, int64_t, int64_t, DiscreteAverageOperation>(
-	    LogicalType::TIMESTAMP_TZ, LogicalType::TIMESTAMP_TZ));
+	                    LogicalType::TIMESTAMP_TZ, LogicalType::TIMESTAMP_TZ)
+	                    .SetStructStateExport(GetAvgStateType));
 	avg.AddFunction(AggregateFunction::UnaryAggregate<AvgState<hugeint_t>, int64_t, int64_t, DiscreteAverageOperation>(
-	    LogicalType::TIME, LogicalType::TIME));
+	                    LogicalType::TIME, LogicalType::TIME)
+	                    .SetStructStateExport(GetAvgStateType));
 	avg.AddFunction(
 	    AggregateFunction::UnaryAggregate<AvgState<hugeint_t>, dtime_tz_t, dtime_tz_t, TimeTZAverageOperation>(
-	        LogicalType::TIME_TZ, LogicalType::TIME_TZ));
+	        LogicalType::TIME_TZ, LogicalType::TIME_TZ)
+	        .SetStructStateExport(GetAvgStateType));
 
 	return avg;
 }
 
 AggregateFunction FAvgFun::GetFunction() {
-	return AggregateFunction::UnaryAggregate<KahanAvgState, double, double, KahanAverageOperation>(LogicalType::DOUBLE,
-	                                                                                               LogicalType::DOUBLE);
+	auto function = AggregateFunction::UnaryAggregate<KahanAvgState, double, double, KahanAverageOperation>(
+	                    LogicalType::DOUBLE, LogicalType::DOUBLE)
+	                    .SetStructStateExport(GetKahanAvgStateType);
+	return function;
 }
 
 } // namespace duckdb
diff --git a/src/duckdb/extension/core_functions/aggregate/algebraic/corr.cpp b/src/duckdb/extension/core_functions/aggregate/algebraic/corr.cpp
@@ -6,8 +6,21 @@
 
 namespace duckdb {
 
+LogicalType GetCorrStateType() {
+	child_list_t<LogicalType> state_children;
+	state_children.emplace_back("cov_pop", CovarPopFun::GetFunction().GetStateType());
+	state_children.emplace_back("dev_pop_x", VarPopFun::GetFunction().GetStateType());
+	state_children.emplace_back("dev_pop_y", VarPopFun::GetFunction().GetStateType());
+	return LogicalType::STRUCT(std::move(state_children));
+}
+
+LogicalType GetCorrExportStateType(const AggregateFunction &) {
+	return GetCorrStateType();
+}
+
 AggregateFunction CorrFun::GetFunction() {
 	return AggregateFunction::BinaryAggregate<CorrState, double, double, double, CorrOperation>(
-	    LogicalType::DOUBLE, LogicalType::DOUBLE, LogicalType::DOUBLE);
+	           LogicalType::DOUBLE, LogicalType::DOUBLE, LogicalType::DOUBLE)
+	    .SetStructStateExport(GetCorrExportStateType);
 }
 } // namespace duckdb
diff --git a/src/duckdb/extension/core_functions/aggregate/algebraic/covar.cpp b/src/duckdb/extension/core_functions/aggregate/algebraic/covar.cpp
@@ -1,17 +1,31 @@
 #include "core_functions/aggregate/algebraic_functions.hpp"
-#include "duckdb/common/types/null_value.hpp"
 #include "core_functions/aggregate/algebraic/covar.hpp"
 
 namespace duckdb {
 
+namespace {
+
+LogicalType GetCovarStateType(const AggregateFunction &) {
+	child_list_t<LogicalType> child_types;
+	child_types.emplace_back("count", LogicalType::UBIGINT);
+	child_types.emplace_back("meanx", LogicalType::DOUBLE);
+	child_types.emplace_back("meany", LogicalType::DOUBLE);
+	child_types.emplace_back("co_moment", LogicalType::DOUBLE);
+	return LogicalType::STRUCT(std::move(child_types));
+}
+
+} // namespace
+
 AggregateFunction CovarPopFun::GetFunction() {
 	return AggregateFunction::BinaryAggregate<CovarState, double, double, double, CovarPopOperation>(
-	    LogicalType::DOUBLE, LogicalType::DOUBLE, LogicalType::DOUBLE);
+	           LogicalType::DOUBLE, LogicalType::DOUBLE, LogicalType::DOUBLE)
+	    .SetStructStateExport(GetCovarStateType);
 }
 
 AggregateFunction CovarSampFun::GetFunction() {
 	return AggregateFunction::BinaryAggregate<CovarState, double, double, double, CovarSampOperation>(
-	    LogicalType::DOUBLE, LogicalType::DOUBLE, LogicalType::DOUBLE);
+	           LogicalType::DOUBLE, LogicalType::DOUBLE, LogicalType::DOUBLE)
+	    .SetStructStateExport(GetCovarStateType);
 }
 
 } // namespace duckdb
diff --git a/src/duckdb/extension/core_functions/aggregate/algebraic/stddev.cpp b/src/duckdb/extension/core_functions/aggregate/algebraic/stddev.cpp
@@ -1,34 +1,49 @@
 #include "core_functions/aggregate/algebraic_functions.hpp"
-#include "duckdb/common/vector_operations/vector_operations.hpp"
 #include "duckdb/function/function_set.hpp"
 #include "core_functions/aggregate/algebraic/stddev.hpp"
-#include <cmath>
 
 namespace duckdb {
 
+namespace {
+
+LogicalType GetStddevStateType(const AggregateFunction &) {
+	child_list_t<LogicalType> child_types;
+	child_types.emplace_back("count", LogicalType::UBIGINT);
+	child_types.emplace_back("mean", LogicalType::DOUBLE);
+	child_types.emplace_back("dsquared", LogicalType::DOUBLE);
+	return LogicalType::STRUCT(std::move(child_types));
+}
+
+} // namespace
+
 AggregateFunction StdDevSampFun::GetFunction() {
 	return AggregateFunction::UnaryAggregate<StddevState, double, double, STDDevSampOperation>(LogicalType::DOUBLE,
-	                                                                                           LogicalType::DOUBLE);
+	                                                                                           LogicalType::DOUBLE)
+	    .SetStructStateExport(GetStddevStateType);
 }
 
 AggregateFunction StdDevPopFun::GetFunction() {
 	return AggregateFunction::UnaryAggregate<StddevState, double, double, STDDevPopOperation>(LogicalType::DOUBLE,
-	                                                                                          LogicalType::DOUBLE);
+	                                                                                          LogicalType::DOUBLE)
+	    .SetStructStateExport(GetStddevStateType);
 }
 
 AggregateFunction VarPopFun::GetFunction() {
 	return AggregateFunction::UnaryAggregate<StddevState, double, double, VarPopOperation>(LogicalType::DOUBLE,
-	                                                                                       LogicalType::DOUBLE);
+	                                                                                       LogicalType::DOUBLE)
+	    .SetStructStateExport(GetStddevStateType);
 }
 
 AggregateFunction VarSampFun::GetFunction() {
 	return AggregateFunction::UnaryAggregate<StddevState, double, double, VarSampOperation>(LogicalType::DOUBLE,
-	                                                                                        LogicalType::DOUBLE);
+	                                                                                        LogicalType::DOUBLE)
+	    .SetStructStateExport(GetStddevStateType);
 }
 
 AggregateFunction StandardErrorOfTheMeanFun::GetFunction() {
 	return AggregateFunction::UnaryAggregate<StddevState, double, double, StandardErrorOfTheMeanOperation>(
-	    LogicalType::DOUBLE, LogicalType::DOUBLE);
+	           LogicalType::DOUBLE, LogicalType::DOUBLE)
+	    .SetStructStateExport(GetStddevStateType);
 }
 
 } // namespace duckdb
diff --git a/src/duckdb/extension/core_functions/aggregate/distributive/approx_count.cpp b/src/duckdb/extension/core_functions/aggregate/distributive/approx_count.cpp
@@ -1,10 +1,6 @@
 #include "duckdb/common/exception.hpp"
-#include "duckdb/common/types/hash.hpp"
 #include "duckdb/common/types/hyperloglog.hpp"
 #include "core_functions/aggregate/distributive_functions.hpp"
-#include "duckdb/function/function_set.hpp"
-#include "duckdb/planner/expression/bound_aggregate_expression.hpp"
-#include "hyperloglog.hpp"
 
 namespace duckdb {
 
@@ -14,7 +10,7 @@ namespace duckdb {
 namespace {
 
 struct ApproxDistinctCountState {
-	HyperLogLog hll;
+	HyperLogLogP<10> hll;
 };
 
 struct ApproxCountDistinctFunction {

diff --git a/src/duckdb/extension/core_functions/aggregate/distributive/bitagg.cpp b/src/duckdb/extension/core_functions/aggregate/distributive/bitagg.cpp
@@ -17,29 +17,57 @@ struct BitState {
 	T value;
 };
 
+template <class T>
+LogicalType GetBitStateType(const AggregateFunction &function) {
+	child_list_t<LogicalType> child_types;
+	child_types.emplace_back("is_set", LogicalType::BOOLEAN);
+
+	LogicalType value_type = function.return_type;
+	child_types.emplace_back("value", value_type);
+
+	return LogicalType::STRUCT(std::move(child_types));
+}
+
+LogicalType GetBitStringStateType(const AggregateFunction &function) {
+	child_list_t<LogicalType> child_types;
+	child_types.emplace_back("is_set", LogicalType::BOOLEAN);
+	child_types.emplace_back("value", function.return_type);
+	return LogicalType::STRUCT(std::move(child_types));
+}
+
 template <class OP>
 AggregateFunction GetBitfieldUnaryAggregate(LogicalType type) {
 	switch (type.id()) {
 	case LogicalTypeId::TINYINT:
-		return AggregateFunction::UnaryAggregate<BitState<uint8_t>, int8_t, int8_t, OP>(type, type);
+		return AggregateFunction::UnaryAggregate<BitState<uint8_t>, int8_t, int8_t, OP>(type, type)
+		    .SetStructStateExport(GetBitStateType<uint8_t>);
 	case LogicalTypeId::SMALLINT:
-		return AggregateFunction::UnaryAggregate<BitState<uint16_t>, int16_t, int16_t, OP>(type, type);
+		return AggregateFunction::UnaryAggregate<BitState<uint16_t>, int16_t, int16_t, OP>(type, type)
+		    .SetStructStateExport(GetBitStateType<uint16_t>);
 	case LogicalTypeId::INTEGER:
-		return AggregateFunction::UnaryAggregate<BitState<uint32_t>, int32_t, int32_t, OP>(type, type);
+		return AggregateFunction::UnaryAggregate<BitState<uint32_t>, int32_t, int32_t, OP>(type, type)
+		    .SetStructStateExport(GetBitStateType<uint32_t>);
 	case LogicalTypeId::BIGINT:
-		return AggregateFunction::UnaryAggregate<BitState<uint64_t>, int64_t, int64_t, OP>(type, type);
+		return AggregateFunction::UnaryAggregate<BitState<uint64_t>, int64_t, int64_t, OP>(type, type)
+		    .SetStructStateExport(GetBitStateType<uint64_t>);
 	case LogicalTypeId::HUGEINT:
-		return AggregateFunction::UnaryAggregate<BitState<hugeint_t>, hugeint_t, hugeint_t, OP>(type, type);
+		return AggregateFunction::UnaryAggregate<BitState<hugeint_t>, hugeint_t, hugeint_t, OP>(type, type)
+		    .SetStructStateExport(GetBitStateType<hugeint_t>);
 	case LogicalTypeId::UTINYINT:
-		return AggregateFunction::UnaryAggregate<BitState<uint8_t>, uint8_t, uint8_t, OP>(type, type);
+		return AggregateFunction::UnaryAggregate<BitState<uint8_t>, uint8_t, uint8_t, OP>(type, type)
+		    .SetStructStateExport(GetBitStateType<uint8_t>);
 	case LogicalTypeId::USMALLINT:
-		return AggregateFunction::UnaryAggregate<BitState<uint16_t>, uint16_t, uint16_t, OP>(type, type);
+		return AggregateFunction::UnaryAggregate<BitState<uint16_t>, uint16_t, uint16_t, OP>(type, type)
+		    .SetStructStateExport(GetBitStateType<uint16_t>);
 	case LogicalTypeId::UINTEGER:
-		return AggregateFunction::UnaryAggregate<BitState<uint32_t>, uint32_t, uint32_t, OP>(type, type);
+		return AggregateFunction::UnaryAggregate<BitState<uint32_t>, uint32_t, uint32_t, OP>(type, type)
+		    .SetStructStateExport(GetBitStateType<uint32_t>);
 	case LogicalTypeId::UBIGINT:
-		return AggregateFunction::UnaryAggregate<BitState<uint64_t>, uint64_t, uint64_t, OP>(type, type);
+		return AggregateFunction::UnaryAggregate<BitState<uint64_t>, uint64_t, uint64_t, OP>(type, type)
+		    .SetStructStateExport(GetBitStateType<uint64_t>);
 	case LogicalTypeId::UHUGEINT:
-		return AggregateFunction::UnaryAggregate<BitState<uhugeint_t>, uhugeint_t, uhugeint_t, OP>(type, type);
+		return AggregateFunction::UnaryAggregate<BitState<uhugeint_t>, uhugeint_t, uhugeint_t, OP>(type, type)
+		    .SetStructStateExport(GetBitStateType<uhugeint_t>);
 	default:
 		throw InternalException("Unimplemented bitfield type for unary aggregate");
 	}
@@ -202,9 +230,11 @@ AggregateFunctionSet BitAndFun::GetFunctions() {
 		bit_and.AddFunction(GetBitfieldUnaryAggregate<BitAndOperation>(type));
 	}
 
-	bit_and.AddFunction(
+	auto bit_string_fun =
 	    AggregateFunction::UnaryAggregateDestructor<BitState<string_t>, string_t, string_t, BitStringAndOperation>(
-	        LogicalType::BIT, LogicalType::BIT));
+	        LogicalType::BIT, LogicalType::BIT);
+	bit_string_fun.SetStructStateExport(GetBitStringStateType);
+	bit_and.AddFunction(bit_string_fun);
 	return bit_and;
 }
 
@@ -213,9 +243,11 @@ AggregateFunctionSet BitOrFun::GetFunctions() {
 	for (auto &type : LogicalType::Integral()) {
 		bit_or.AddFunction(GetBitfieldUnaryAggregate<BitOrOperation>(type));
 	}
-	bit_or.AddFunction(
+	auto bit_string_fun =
 	    AggregateFunction::UnaryAggregateDestructor<BitState<string_t>, string_t, string_t, BitStringOrOperation>(
-	        LogicalType::BIT, LogicalType::BIT));
+	        LogicalType::BIT, LogicalType::BIT);
+	bit_string_fun.SetStructStateExport(GetBitStringStateType);
+	bit_or.AddFunction(bit_string_fun);
 	return bit_or;
 }
 
@@ -224,9 +256,11 @@ AggregateFunctionSet BitXorFun::GetFunctions() {
 	for (auto &type : LogicalType::Integral()) {
 		bit_xor.AddFunction(GetBitfieldUnaryAggregate<BitXorOperation>(type));
 	}
-	bit_xor.AddFunction(
+	auto bit_string_fun =
 	    AggregateFunction::UnaryAggregateDestructor<BitState<string_t>, string_t, string_t, BitStringXorOperation>(
-	        LogicalType::BIT, LogicalType::BIT));
+	        LogicalType::BIT, LogicalType::BIT);
+	bit_string_fun.SetStructStateExport(GetBitStringStateType);
+	bit_xor.AddFunction(bit_string_fun);
 	return bit_xor;
 }
 

diff --git a/src/duckdb/extension/core_functions/aggregate/distributive/bool.cpp b/src/duckdb/extension/core_functions/aggregate/distributive/bool.cpp
@@ -93,22 +93,29 @@ struct BoolOrFunFunction {
 	}
 };
 
+LogicalType GetBoolAndStateType(const AggregateFunction &function) {
+	child_list_t<LogicalType> child_types;
+	child_types.emplace_back("empty", LogicalType::BOOLEAN);
+	child_types.emplace_back("val", LogicalType::BOOLEAN);
+	return LogicalType::STRUCT(std::move(child_types));
+}
+
 } // namespace
 
 AggregateFunction BoolOrFun::GetFunction() {
 	auto fun = AggregateFunction::UnaryAggregate<BoolState, bool, bool, BoolOrFunFunction>(
 	    LogicalType(LogicalTypeId::BOOLEAN), LogicalType::BOOLEAN);
 	fun.SetOrderDependent(AggregateOrderDependent::NOT_ORDER_DEPENDENT);
 	fun.SetDistinctDependent(AggregateDistinctDependent::NOT_DISTINCT_DEPENDENT);
-	return fun;
+	return fun.SetStructStateExport(GetBoolAndStateType);
 }
 
 AggregateFunction BoolAndFun::GetFunction() {
 	auto fun = AggregateFunction::UnaryAggregate<BoolState, bool, bool, BoolAndFunFunction>(
 	    LogicalType(LogicalTypeId::BOOLEAN), LogicalType::BOOLEAN);
 	fun.SetOrderDependent(AggregateOrderDependent::NOT_ORDER_DEPENDENT);
 	fun.SetDistinctDependent(AggregateDistinctDependent::NOT_DISTINCT_DEPENDENT);
-	return fun;
+	return fun.SetStructStateExport(GetBoolAndStateType);
 }
 
 } // namespace duckdb