risingwavelabs · Honeta · Mar 30, 2023 · Mar 29, 2023 · Mar 30, 2023
diff --git a/proto/expr.proto b/proto/expr.proto
@@ -131,6 +131,7 @@ message ExprNode {
     FORMAT_TYPE = 534;
     ARRAY_DISTINCT = 535;
     ARRAY_LENGTH = 536;
+    CARDINALITY = 537;
 
     // Jsonb functions
 

diff --git a/src/expr/src/expr/expr_cardinality.rs b/src/expr/src/expr/expr_cardinality.rs
@@ -0,0 +1,63 @@
+// Copyright 2023 RisingWave Labs
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use risingwave_common::array::ListRef;
+use risingwave_expr_macro::function;
+
+/// Returns the total number of elements in the array.
+///
+/// ```sql
+/// cardinality ( array anyarray) → int64
+/// ```
+///
+/// Examples:
+///
+/// ```slt
+/// query T
+/// select cardinality(null::int[]);
+/// ----
+/// NULL
+///
+/// query T
+/// select cardinality(array[1,2,3]);
+/// ----
+/// 3
+///
+/// query T
+/// select cardinality(array[1,2,3,4,1]);
+/// ----
+/// 5
+///
+/// query T
+/// select cardinality(array[array[1, 2, 3]]);
+/// ----
+/// 3
+///
+/// query T
+/// select cardinality(array[array[array[3,4,5],array[2,2,2]],array[array[6,7,8],array[0,0,0]]]);
+/// ----
+/// 12
+///
+/// query T
+/// select cardinality(array[NULL]);
+/// ----
+/// 1
+///
+/// query error unknown type
+/// select cardinality(null);
+/// ```
+#[function("cardinality(list) -> int64")]
+fn cardinality(array: ListRef<'_>) -> i64 {
+    array.flatten().len() as _
+}
diff --git a/src/expr/src/expr/mod.rs b/src/expr/src/expr/mod.rs
@@ -38,6 +38,7 @@ mod expr_array_length;
 mod expr_array_to_string;
 mod expr_binary_nonnull;
 mod expr_binary_nullable;
+mod expr_cardinality;
 mod expr_case;
 mod expr_coalesce;
 mod expr_concat_ws;

diff --git a/src/frontend/src/binder/expr/function.rs b/src/frontend/src/binder/expr/function.rs
@@ -398,6 +398,7 @@ impl Binder {
                 ("array_to_string", raw_call(ExprType::ArrayToString)),
                 ("array_distinct", raw_call(ExprType::ArrayDistinct)),
                 ("array_length", raw_call(ExprType::ArrayLength)),
+                ("cardinality", raw_call(ExprType::Cardinality)),
                 // jsonb
                 ("jsonb_object_field", raw_call(ExprType::JsonbAccessInner)),
                 ("jsonb_array_element", raw_call(ExprType::JsonbAccessInner)),

diff --git a/src/frontend/src/expr/type_inference/func.rs b/src/frontend/src/expr/type_inference/func.rs
@@ -577,6 +577,24 @@ fn infer_type_for_special(
                 _ => Ok(None),
             }
         }
+        ExprType::Cardinality => {
+            ensure_arity!("cardinality", | inputs | == 1);
+            let return_type = inputs[0].return_type();
+
+            if inputs[0].is_unknown() {
+                return Err(ErrorCode::BindError(
+                    "Cannot get cardinality of unknown type".to_string(),
+                )
+                .into());
+            }
+
+            match return_type {
+                DataType::List {
+                    datatype: _list_elem_type,
+                } => Ok(Some(DataType::Int64)),
+                _ => Ok(None),
+            }
+        }
         ExprType::Vnode => {
             ensure_arity!("vnode", 1 <= | inputs |);
             Ok(Some(DataType::Int16))