feat: add isnull function

src/common/function/src/function_registry.rs

@@ -21,6 +21,7 @@ use once_cell::sync::Lazy;
 use crate::function::FunctionRef;
 use crate::scalars::aggregate::{AggregateFunctionMetaRef, AggregateFunctions};
 use crate::scalars::date::DateFunction;
+use crate::scalars::expression::ExpressionFunction;
 use crate::scalars::math::MathFunction;
 use crate::scalars::numpy::NumpyFunction;
 use crate::scalars::timestamp::TimestampFunction;
@@ -80,6 +81,7 @@ pub static FUNCTION_REGISTRY: Lazy<Arc<FunctionRegistry>> = Lazy::new(|| {
     NumpyFunction::register(&function_registry);
     TimestampFunction::register(&function_registry);
     DateFunction::register(&function_registry);
+    ExpressionFunction::register(&function_registry);
 
     // Aggregate functions
     AggregateFunctions::register(&function_registry);

src/common/function/src/scalars/expression.rs

@@ -14,8 +14,22 @@
 
 mod binary;
 mod ctx;
+mod is_null;
 mod unary;
 
+use std::sync::Arc;
+
 pub use binary::scalar_binary_op;
 pub use ctx::EvalContext;
 pub use unary::scalar_unary_op;
+
+use crate::function_registry::FunctionRegistry;
+use crate::scalars::expression::is_null::IsNullFunction;
+
+pub(crate) struct ExpressionFunction;
+
+impl ExpressionFunction {
+    pub fn register(registry: &FunctionRegistry) {
+        registry.register(Arc::new(IsNullFunction));
+    }
+}

src/common/function/src/scalars/expression/is_null.rs

@@ -0,0 +1,109 @@
+// Copyright 2023 Greptime Team
+//
+// 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 std::fmt;
+use std::fmt::Display;
+use std::sync::Arc;
+
+use common_query::error;
+use common_query::error::{ArrowComputeSnafu, InvalidFuncArgsSnafu};
+use common_query::prelude::{Signature, Volatility};
+use datafusion::arrow::array::ArrayRef;
+use datafusion::arrow::compute::is_null;
+use datatypes::data_type::ConcreteDataType;
+use datatypes::prelude::VectorRef;
+use datatypes::vectors::Helper;
+use snafu::{ensure, ResultExt};
+
+use crate::function::{Function, FunctionContext};
+
+const NAME: &str = "isnull";
+
+/// The function to check whether an expression is NULL
+#[derive(Clone, Debug, Default)]
+pub struct IsNullFunction;
+
+impl Display for IsNullFunction {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", NAME.to_ascii_uppercase())
+    }
+}
+
+impl Function for IsNullFunction {
+    fn name(&self) -> &str {
+        NAME
+    }
+
+    fn return_type(&self, _: &[ConcreteDataType]) -> common_query::error::Result<ConcreteDataType> {
+        Ok(ConcreteDataType::boolean_datatype())
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::any(1, Volatility::Immutable)
+    }
+
+    fn eval(
+        &self,
+        _func_ctx: FunctionContext,
+        columns: &[VectorRef],
+    ) -> common_query::error::Result<VectorRef> {
+        ensure!(
+            columns.len() == 1,
+            InvalidFuncArgsSnafu {
+                err_msg: format!(
+                    "The length of the args is not correct, expect exactly one, have: {}",
+                    columns.len()
+                ),
+            }
+        );
+        let values = &columns[0];
+        let arrow_array = &values.to_arrow_array();
+        let result = is_null(arrow_array).context(ArrowComputeSnafu)?;
+
+        Helper::try_into_vector(Arc::new(result) as ArrayRef).context(error::FromArrowArraySnafu)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::sync::Arc;
+
+    use common_query::prelude::TypeSignature;
+    use datatypes::scalars::ScalarVector;
+    use datatypes::vectors::{BooleanVector, Float32Vector};
+
+    use super::*;
+    #[test]
+    fn test_is_null_function() {
+        let is_null = IsNullFunction;
+        assert_eq!("isnull", is_null.name());
+        assert_eq!(
+            ConcreteDataType::boolean_datatype(),
+            is_null.return_type(&[]).unwrap()
+        );
+        assert_eq!(
+            is_null.signature(),
+            Signature {
+                type_signature: TypeSignature::Any(1),
+                volatility: Volatility::Immutable
+            }
+        );
+        let values = vec![None, Some(3.0), None];
+
+        let args: Vec<VectorRef> = vec![Arc::new(Float32Vector::from(values))];
+        let vector = is_null.eval(FunctionContext::default(), &args).unwrap();
+        let expect: VectorRef = Arc::new(BooleanVector::from_vec(vec![true, false, true]));
+        assert_eq!(expect, vector);
+    }
+}

tests/cases/standalone/common/function/expression.result

@@ -0,0 +1,70 @@
+CREATE TABLE t(a INTEGER, ts timestamp time index);
+
+Affected Rows: 0
+
+INSERT INTO t VALUES (1, 1), (null, 2), (3, 3);
+
+Affected Rows: 3
+
+SELECT ISNULL(a) from t;
+
++-------------+
+| isnull(t.a) |
++-------------+
+| false       |
+| true        |
+| false       |
++-------------+
+
+SELECT ISNULL(null);
+
++--------------+
+| isnull(NULL) |
++--------------+
+| true         |
++--------------+
+
+SELECT ISNULL(1);
+
++------------------+
+| isnull(Int64(1)) |
++------------------+
+| false            |
++------------------+
+
+SELECT ISNULL(-1);
+
++-------------------+
+| isnull(Int64(-1)) |
++-------------------+
+| false             |
++-------------------+
+
+SELECT ISNULL(1.0);
+
++--------------------+
+| isnull(Float64(1)) |
++--------------------+
+| false              |
++--------------------+
+
+SELECT ISNULL(true);
+
++-----------------------+
+| isnull(Boolean(true)) |
++-----------------------+
+| false                 |
++-----------------------+
+
+SELECT ISNULL('string');
+
++------------------------+
+| isnull(Utf8("string")) |
++------------------------+
+| false                  |
++------------------------+
+
+DROP TABLE t;
+
+Affected Rows: 0
+

tests/cases/standalone/common/function/expression.sql

@@ -0,0 +1,19 @@
+CREATE TABLE t(a INTEGER, ts timestamp time index);
+
+INSERT INTO t VALUES (1, 1), (null, 2), (3, 3);
+
+SELECT ISNULL(a) from t;
+
+SELECT ISNULL(null);
+
+SELECT ISNULL(1);
+
+SELECT ISNULL(-1);
+
+SELECT ISNULL(1.0);
+
+SELECT ISNULL(true);
+
+SELECT ISNULL('string');
+
+DROP TABLE t;