fix return field for is_null and is_not_null expression (#17056)

Author: davidhewitt

datafusion/physical-expr/src/expressions/is_not_null.rs

@@ -18,7 +18,6 @@
 //! IS NOT NULL expression
 
 use crate::PhysicalExpr;
-use arrow::datatypes::FieldRef;
 use arrow::{
     datatypes::{DataType, Schema},
     record_batch::RecordBatch,
@@ -94,10 +93,6 @@ impl PhysicalExpr for IsNotNullExpr {
         }
     }
 
-    fn return_field(&self, input_schema: &Schema) -> Result<FieldRef> {
-        self.arg.return_field(input_schema)
-    }
-
     fn children(&self) -> Vec<&Arc<dyn PhysicalExpr>> {
         vec![&self.arg]
     }

datafusion/physical-expr/src/expressions/is_null.rs

@@ -18,7 +18,6 @@
 //! IS NULL expression
 
 use crate::PhysicalExpr;
-use arrow::datatypes::FieldRef;
 use arrow::{
     datatypes::{DataType, Schema},
     record_batch::RecordBatch,
@@ -93,10 +92,6 @@ impl PhysicalExpr for IsNullExpr {
         }
     }
 
-    fn return_field(&self, input_schema: &Schema) -> Result<FieldRef> {
-        self.arg.return_field(input_schema)
-    }
-
     fn children(&self) -> Vec<&Arc<dyn PhysicalExpr>> {
         vec![&self.arg]
     }

datafusion/sqllogictest/test_files/expr.slt

@@ -2131,3 +2131,26 @@ query T
 select E'foo\t\tbar';
 ----
 foo		bar
+
+statement ok
+create table t (a float) as values (1), (null), (3);
+
+# https://github.com/apache/datafusion/issues/17055
+# is not null did not correctly infer as boolean in udf argument position
+query B
+select greatest(a is not null, false) from t;
+----
+true
+false
+true
+
+# same for is null
+query B
+select greatest(a is null, false) from t;
+----
+false
+true
+false
+
+statement ok
+drop table t;