From 069118bef40b63549f4771e03ea1452a9293ee05 Mon Sep 17 00:00:00 2001
From: pchintar <89355405+pchintar@users.noreply.github.com>
Date: Fri, 5 Jun 2026 15:03:43 +0530
Subject: [PATCH] Coerce aggregate FILTER predicates to boolean

---
 .../optimizer/src/analyzer/type_coercion.rs   | 11 ++++++
 .../sqllogictest/test_files/aggregate.slt     | 34 +++++++++++++++++++
 2 files changed, 45 insertions(+)

diff --git a/datafusion/optimizer/src/analyzer/type_coercion.rs b/datafusion/optimizer/src/analyzer/type_coercion.rs
index df3ccc282564c..032fe2524096e 100644
--- a/datafusion/optimizer/src/analyzer/type_coercion.rs
+++ b/datafusion/optimizer/src/analyzer/type_coercion.rs
@@ -715,6 +715,12 @@ impl TreeNodeRewriter for TypeCoercionRewriter<'_> {
             }) => {
                 let new_expr =
                     coerce_arguments_for_signature(args, self.schema, func.as_ref())?;
+
+                let filter = filter
+                    .map(|filter| filter.cast_to(&DataType::Boolean, self.schema))
+                    .transpose()?
+                    .map(Box::new);
+
                 Ok(Transformed::yes(Expr::AggregateFunction(
                     expr::AggregateFunction::new_udf(
                         func,
@@ -752,6 +758,11 @@ impl TreeNodeRewriter for TypeCoercionRewriter<'_> {
                     }
                 };
 
+                let filter = filter
+                    .map(|filter| filter.cast_to(&DataType::Boolean, self.schema))
+                    .transpose()?
+                    .map(Box::new);
+
                 let new_expr = Expr::from(WindowFunction {
                     fun,
                     params: expr::WindowFunctionParams {
diff --git a/datafusion/sqllogictest/test_files/aggregate.slt b/datafusion/sqllogictest/test_files/aggregate.slt
index 2861b50580407..35ffdbeeeca09 100644
--- a/datafusion/sqllogictest/test_files/aggregate.slt
+++ b/datafusion/sqllogictest/test_files/aggregate.slt
@@ -6266,6 +6266,40 @@ GROUP BY g
 ----
 0 0
 
+# query_with_untyped_null_filter
+query I
+SELECT count(*) FILTER (WHERE NULL)
+----
+0
+
+query I
+SELECT count(1) FILTER (WHERE NULL)
+----
+0
+
+query I
+SELECT sum(1) FILTER (WHERE NULL)
+----
+NULL
+
+query R
+SELECT avg(1) FILTER (WHERE NULL)
+----
+NULL
+
+# window_aggregate_with_untyped_null_filter
+query I
+SELECT count(*) FILTER (WHERE NULL) OVER ()
+FROM (VALUES (1)) AS t(x)
+----
+0
+
+query I
+SELECT sum(1) FILTER (WHERE NULL) OVER ()
+FROM (VALUES (1)) AS t(x)
+----
+NULL
+
 # query_with_and_without_filter
 query III rowsort
 SELECT