datafusion_functions/datetime/
now.rs

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// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you 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 arrow::datatypes::DataType;
use arrow::datatypes::DataType::Timestamp;
use arrow::datatypes::TimeUnit::Nanosecond;
use std::any::Any;

use datafusion_common::{internal_err, Result, ScalarValue};
use datafusion_expr::simplify::{ExprSimplifyResult, SimplifyInfo};
use datafusion_expr::{
    ColumnarValue, Documentation, Expr, ReturnInfo, ReturnTypeArgs, ScalarUDFImpl,
    Signature, Volatility,
};
use datafusion_macros::user_doc;

#[user_doc(
    doc_section(label = "Time and Date Functions"),
    description = r#"
Returns the current UTC timestamp.

The `now()` return value is determined at query time and will return the same timestamp, no matter when in the query plan the function executes.
"#,
    syntax_example = "now()"
)]
#[derive(Debug)]
pub struct NowFunc {
    signature: Signature,
    aliases: Vec<String>,
}

impl Default for NowFunc {
    fn default() -> Self {
        Self::new()
    }
}

impl NowFunc {
    pub fn new() -> Self {
        Self {
            signature: Signature::nullary(Volatility::Stable),
            aliases: vec!["current_timestamp".to_string()],
        }
    }
}

/// Create an implementation of `now()` that always returns the
/// specified timestamp.
///
/// The semantics of `now()` require it to return the same value
/// wherever it appears within a single statement. This value is
/// chosen during planning time.
impl ScalarUDFImpl for NowFunc {
    fn as_any(&self) -> &dyn Any {
        self
    }

    fn name(&self) -> &str {
        "now"
    }

    fn signature(&self) -> &Signature {
        &self.signature
    }

    fn return_type_from_args(&self, _args: ReturnTypeArgs) -> Result<ReturnInfo> {
        Ok(ReturnInfo::new_non_nullable(Timestamp(
            Nanosecond,
            Some("+00:00".into()),
        )))
    }

    fn return_type(&self, _arg_types: &[DataType]) -> Result<DataType> {
        internal_err!("return_type_from_args should be called instead")
    }

    fn invoke_batch(
        &self,
        _args: &[ColumnarValue],
        _number_rows: usize,
    ) -> Result<ColumnarValue> {
        internal_err!("invoke should not be called on a simplified now() function")
    }

    fn simplify(
        &self,
        _args: Vec<Expr>,
        info: &dyn SimplifyInfo,
    ) -> Result<ExprSimplifyResult> {
        let now_ts = info
            .execution_props()
            .query_execution_start_time
            .timestamp_nanos_opt();
        Ok(ExprSimplifyResult::Simplified(Expr::Literal(
            ScalarValue::TimestampNanosecond(now_ts, Some("+00:00".into())),
        )))
    }

    fn aliases(&self) -> &[String] {
        &self.aliases
    }

    fn documentation(&self) -> Option<&Documentation> {
        self.doc()
    }
}