feat: support greatest function (#2490)

* feat: support greatest function

* feat: make greatest take date_type as input

* fix: move sqlness test into common/function/time.sql

* fix: avoid using unwarp

* fix: use downcast

* refactor: simplify arrow cast

src/common/function/src/scalars/timestamp.rs

@@ -12,8 +12,10 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 use std::sync::Arc;
+mod greatest;
 mod to_unixtime;
 
+use greatest::GreatestFunction;
 use to_unixtime::ToUnixtimeFunction;
 
 use crate::scalars::function_registry::FunctionRegistry;
@@ -23,5 +25,6 @@ pub(crate) struct TimestampFunction;
 impl TimestampFunction {
     pub fn register(registry: &FunctionRegistry) {
         registry.register(Arc::new(ToUnixtimeFunction));
+        registry.register(Arc::new(GreatestFunction));
     }
 }

src/common/function/src/scalars/timestamp/greatest.rs

@@ -0,0 +1,175 @@
+// 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::{self};
+
+use common_query::error::{
+    self, ArrowComputeSnafu, InvalidFuncArgsSnafu, Result, UnsupportedInputDataTypeSnafu,
+};
+use common_query::prelude::{Signature, Volatility};
+use datatypes::arrow::array::AsArray;
+use datatypes::arrow::compute::cast;
+use datatypes::arrow::compute::kernels::comparison::gt_dyn;
+use datatypes::arrow::compute::kernels::zip;
+use datatypes::arrow::datatypes::{DataType as ArrowDataType, Date32Type};
+use datatypes::prelude::ConcreteDataType;
+use datatypes::vectors::{Helper, VectorRef};
+use snafu::{ensure, ResultExt};
+
+use crate::scalars::function::{Function, FunctionContext};
+
+#[derive(Clone, Debug, Default)]
+pub struct GreatestFunction;
+
+const NAME: &str = "greatest";
+
+impl Function for GreatestFunction {
+    fn name(&self) -> &str {
+        NAME
+    }
+
+    fn return_type(&self, _input_types: &[ConcreteDataType]) -> Result<ConcreteDataType> {
+        Ok(ConcreteDataType::date_datatype())
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::uniform(
+            2,
+            vec![
+                ConcreteDataType::string_datatype(),
+                ConcreteDataType::date_datatype(),
+            ],
+            Volatility::Immutable,
+        )
+    }
+
+    fn eval(&self, _func_ctx: FunctionContext, columns: &[VectorRef]) -> Result<VectorRef> {
+        ensure!(
+            columns.len() == 2,
+            InvalidFuncArgsSnafu {
+                err_msg: format!(
+                    "The length of the args is not correct, expect exactly two, have: {}",
+                    columns.len()
+                ),
+            }
+        );
+        match columns[0].data_type() {
+            ConcreteDataType::String(_) => {
+                let column1 = cast(&columns[0].to_arrow_array(), &ArrowDataType::Date32)
+                    .context(ArrowComputeSnafu)?;
+                let column1 = column1.as_primitive::<Date32Type>();
+                let column2 = cast(&columns[1].to_arrow_array(), &ArrowDataType::Date32)
+                    .context(ArrowComputeSnafu)?;
+                let column2 = column2.as_primitive::<Date32Type>();
+                let boolean_array = gt_dyn(&column1, &column2).context(ArrowComputeSnafu)?;
+                let result =
+                    zip::zip(&boolean_array, &column1, &column2).context(ArrowComputeSnafu)?;
+                Ok(Helper::try_into_vector(&result).context(error::FromArrowArraySnafu)?)
+            }
+            ConcreteDataType::Date(_) => {
+                let column1 = columns[0].to_arrow_array();
+                let column1 = column1.as_primitive::<Date32Type>();
+                let column2 = columns[1].to_arrow_array();
+                let column2 = column2.as_primitive::<Date32Type>();
+                let boolean_array = gt_dyn(&column1, &column2).context(ArrowComputeSnafu)?;
+                let result =
+                    zip::zip(&boolean_array, &column1, &column2).context(ArrowComputeSnafu)?;
+                Ok(Helper::try_into_vector(&result).context(error::FromArrowArraySnafu)?)
+            }
+            _ => UnsupportedInputDataTypeSnafu {
+                function: NAME,
+                datatypes: columns.iter().map(|c| c.data_type()).collect::<Vec<_>>(),
+            }
+            .fail(),
+        }
+    }
+}
+
+impl fmt::Display for GreatestFunction {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "GREATEST")
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::str::FromStr;
+    use std::sync::Arc;
+
+    use common_time::Date;
+    use datatypes::prelude::ConcreteDataType;
+    use datatypes::types::DateType;
+    use datatypes::value::Value;
+    use datatypes::vectors::{DateVector, StringVector, Vector};
+
+    use super::GreatestFunction;
+    use crate::scalars::function::FunctionContext;
+    use crate::scalars::Function;
+
+    #[test]
+    fn test_greatest_takes_string_vector() {
+        let function = GreatestFunction;
+        assert_eq!(
+            function.return_type(&[]).unwrap(),
+            ConcreteDataType::Date(DateType)
+        );
+        let columns = vec![
+            Arc::new(StringVector::from(vec![
+                "1970-01-01".to_string(),
+                "2012-12-23".to_string(),
+            ])) as _,
+            Arc::new(StringVector::from(vec![
+                "2001-02-01".to_string(),
+                "1999-01-01".to_string(),
+            ])) as _,
+        ];
+
+        let result = function.eval(FunctionContext::default(), &columns).unwrap();
+        let result = result.as_any().downcast_ref::<DateVector>().unwrap();
+        assert_eq!(result.len(), 2);
+        assert_eq!(
+            result.get(0),
+            Value::Date(Date::from_str("2001-02-01").unwrap())
+        );
+        assert_eq!(
+            result.get(1),
+            Value::Date(Date::from_str("2012-12-23").unwrap())
+        );
+    }
+
+    #[test]
+    fn test_greatest_takes_date_vector() {
+        let function = GreatestFunction;
+        assert_eq!(
+            function.return_type(&[]).unwrap(),
+            ConcreteDataType::Date(DateType)
+        );
+        let columns = vec![
+            Arc::new(DateVector::from_slice(vec![-1, 2])) as _,
+            Arc::new(DateVector::from_slice(vec![0, 1])) as _,
+        ];
+
+        let result = function.eval(FunctionContext::default(), &columns).unwrap();
+        let result = result.as_any().downcast_ref::<DateVector>().unwrap();
+        assert_eq!(result.len(), 2);
+        assert_eq!(
+            result.get(0),
+            Value::Date(Date::from_str("1970-01-01").unwrap())
+        );
+        assert_eq!(
+            result.get(1),
+            Value::Date(Date::from_str("1970-01-03").unwrap())
+        );
+    }
+}

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

@@ -4,3 +4,19 @@ select current_time();
 
 ++|current_time()|++|TIME|++
 
+select GREATEST('1999-01-30', '2023-03-01');
+
++-------------------------------------------------+
+| greatest(Utf8("1999-01-30"),Utf8("2023-03-01")) |
++-------------------------------------------------+
+| 2023-03-01                                      |
++-------------------------------------------------+
+
+select GREATEST('2000-02-11'::Date, '2020-12-30'::Date);
+
++-------------------------------------------------+
+| greatest(Utf8("2000-02-11"),Utf8("2020-12-30")) |
++-------------------------------------------------+
+| 2020-12-30                                      |
++-------------------------------------------------+
+

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

@@ -1,3 +1,7 @@
 -- SQLNESS REPLACE (\d+:\d+:\d+\.\d+) TIME
 -- SQLNESS REPLACE [\s\-]+
 select current_time();
+
+select GREATEST('1999-01-30', '2023-03-01');
+
+select GREATEST('2000-02-11'::Date, '2020-12-30'::Date);

tests/cases/standalone/common/select/dummy.sql

@@ -31,4 +31,3 @@ select b from test_unixtime;
 select TO_UNIXTIME(b) from test_unixtime;
 
 DROP TABLE test_unixtime;
-