init draft (#8625)

Signed-off-by: jayzhan211 <jayzhan211@gmail.com>

datafusion/expr/src/built_in_function.rs

@@ -960,7 +960,10 @@ impl BuiltinScalarFunction {
                 Signature::variadic_any(self.volatility())
             }
             BuiltinScalarFunction::ArrayPositions => Signature::any(2, self.volatility()),
-            BuiltinScalarFunction::ArrayPrepend => Signature::any(2, self.volatility()),
+            BuiltinScalarFunction::ArrayPrepend => Signature {
+                type_signature: ElementAndArray,
+                volatility: self.volatility(),
+            },
             BuiltinScalarFunction::ArrayRepeat => Signature::any(2, self.volatility()),
             BuiltinScalarFunction::ArrayRemove => Signature::any(2, self.volatility()),
             BuiltinScalarFunction::ArrayRemoveN => Signature::any(3, self.volatility()),

datafusion/expr/src/signature.rs

@@ -122,6 +122,10 @@ pub enum TypeSignature {
     /// List dimension of the List/LargeList is equivalent to the number of List.
     /// List dimension of the non-list is 0.
     ArrayAndElement,
+    /// Specialized Signature for ArrayPrepend and similar functions
+    /// The first argument should be non-list or list, and the second argument should be List/LargeList.
+    /// The first argument's list dimension should be one dimension less than the second argument's list dimension.
+    ElementAndArray,
 }
 
 impl TypeSignature {
@@ -155,6 +159,9 @@ impl TypeSignature {
             TypeSignature::ArrayAndElement => {
                 vec!["ArrayAndElement(List<T>, T)".to_string()]
             }
+            TypeSignature::ElementAndArray => {
+                vec!["ElementAndArray(T, List<T>)".to_string()]
+            }
         }
     }
 

datafusion/expr/src/type_coercion/functions.rs

@@ -79,6 +79,55 @@ fn get_valid_types(
     signature: &TypeSignature,
     current_types: &[DataType],
 ) -> Result<Vec<Vec<DataType>>> {
+    fn array_append_or_prepend_valid_types(
+        current_types: &[DataType],
+        is_append: bool,
+    ) -> Result<Vec<Vec<DataType>>> {
+        if current_types.len() != 2 {
+            return Ok(vec![vec![]]);
+        }
+
+        let (array_type, elem_type) = if is_append {
+            (&current_types[0], &current_types[1])
+        } else {
+            (&current_types[1], &current_types[0])
+        };
+
+        // We follow Postgres on `array_append(Null, T)`, which is not valid.
+        if array_type.eq(&DataType::Null) {
+            return Ok(vec![vec![]]);
+        }
+
+        // We need to find the coerced base type, mainly for cases like:
+        // `array_append(List(null), i64)` -> `List(i64)`
+        let array_base_type = datafusion_common::utils::base_type(array_type);
+        let elem_base_type = datafusion_common::utils::base_type(elem_type);
+        let new_base_type = comparison_coercion(&array_base_type, &elem_base_type);
+
+        if new_base_type.is_none() {
+            return internal_err!(
+                "Coercion from {array_base_type:?} to {elem_base_type:?} not supported."
+            );
+        }
+        let new_base_type = new_base_type.unwrap();
+
+        let array_type = datafusion_common::utils::coerced_type_with_base_type_only(
+            array_type,
+            &new_base_type,
+        );
+
+        if let DataType::List(ref field) = array_type {
+            let elem_type = field.data_type();
+            if is_append {
+                Ok(vec![vec![array_type.clone(), elem_type.to_owned()]])
+            } else {
+                Ok(vec![vec![elem_type.to_owned(), array_type.clone()]])
+            }
+        } else {
+            Ok(vec![vec![]])
+        }
+    }
+
     let valid_types = match signature {
         TypeSignature::Variadic(valid_types) => valid_types
             .iter()
@@ -112,42 +161,10 @@ fn get_valid_types(
 
         TypeSignature::Exact(valid_types) => vec![valid_types.clone()],
         TypeSignature::ArrayAndElement => {
-            if current_types.len() != 2 {
-                return Ok(vec![vec![]]);
-            }
-
-            let array_type = &current_types[0];
-            let elem_type = &current_types[1];
-
-            // We follow Postgres on `array_append(Null, T)`, which is not valid.
-            if array_type.eq(&DataType::Null) {
-                return Ok(vec![vec![]]);
-            }
-
-            // We need to find the coerced base type, mainly for cases like:
-            // `array_append(List(null), i64)` -> `List(i64)`
-            let array_base_type = datafusion_common::utils::base_type(array_type);
-            let elem_base_type = datafusion_common::utils::base_type(elem_type);
-            let new_base_type = comparison_coercion(&array_base_type, &elem_base_type);
-
-            if new_base_type.is_none() {
-                return internal_err!(
-                    "Coercion from {array_base_type:?} to {elem_base_type:?} not supported."
-                );
-            }
-            let new_base_type = new_base_type.unwrap();
-
-            let array_type = datafusion_common::utils::coerced_type_with_base_type_only(
-                array_type,
-                &new_base_type,
-            );
-
-            if let DataType::List(ref field) = array_type {
-                let elem_type = field.data_type();
-                return Ok(vec![vec![array_type.clone(), elem_type.to_owned()]]);
-            } else {
-                return Ok(vec![vec![]]);
-            }
+            return array_append_or_prepend_valid_types(current_types, true)
+        }
+        TypeSignature::ElementAndArray => {
+            return array_append_or_prepend_valid_types(current_types, false)
         }
         TypeSignature::Any(number) => {
             if current_types.len() != *number {

datafusion/sqllogictest/test_files/array.slt

@@ -1618,18 +1618,58 @@ select array_append(column1, make_array(1, 11, 111)), array_append(make_array(ma
 
 ## array_prepend (aliases: `list_prepend`, `array_push_front`, `list_push_front`)
 
-# TODO: array_prepend with NULLs
-# array_prepend scalar function #1
-# query ?
-# select array_prepend(4, make_array());
-# ----
-# [4]
+# array_prepend with NULLs
+
+# DuckDB: [4]
+# ClickHouse: Null
+# Since they dont have the same result, we just follow Postgres, return error
+query error
+select array_prepend(4, NULL);
+
+query ?
+select array_prepend(4, []);
+----
+[4]
+
+query ?
+select array_prepend(4, [null]);
+----
+[4, ]
+
+# DuckDB: [null]
+# ClickHouse: [null]
+query ?
+select array_prepend(null, []);
+----
+[]
+
+query ?
+select array_prepend(null, [1]);
+----
+[, 1]
+
+query ?
+select array_prepend(null, [[1,2,3]]);
+----
+[, [1, 2, 3]]
+
+# DuckDB: [[]]
+# ClickHouse: [[]]
+# TODO: We may also return [[]]
+query error
+select array_prepend([], []);
+
+# DuckDB: [null]
+# ClickHouse: [null]
+# TODO: We may also return [null]
+query error
+select array_prepend(null, null);
+
+query ?
+select array_append([], null);
+----
+[]
 
-# array_prepend scalar function #2
-# query ??
-# select array_prepend(make_array(), make_array()), array_prepend(make_array(4), make_array());
-# ----
-# [[]] [[4]]
 
 # array_prepend scalar function #3
 query ???