dayname scalar function

crates/embucket-functions/src/datetime/dayname.rs

@@ -0,0 +1,143 @@
+use chrono::{DateTime, Datelike, NaiveDateTime, Utc};
+use datafusion::arrow::array::{Array, StringBuilder};
+use datafusion::arrow::datatypes::{DataType, TimeUnit};
+use datafusion::error::Result as DFResult;
+use datafusion::logical_expr::TypeSignature::{Coercible, Exact};
+use datafusion::logical_expr::{Coercion, ColumnarValue, TypeSignatureClass};
+use datafusion_common::{ScalarValue, exec_err};
+use datafusion_expr::{ScalarFunctionArgs, ScalarUDFImpl, Signature, Volatility};
+use std::any::Any;
+use std::sync::Arc;
+
+/// `DAYNAME` SQL function
+///
+/// Extracts the three-letter day-of-week name from the specified date or timestamp.
+///
+/// Syntax: `DAYNAME(<date_or_timestamp>)`
+///
+/// Arguments:
+/// - `date_or_timestamp`: A date or timestamp value.
+///
+/// Example: `SELECT dayname('2025-05-08T23:39:20.123-07:00'::timestamp) AS value;`
+///
+/// Returns:
+/// - Returns a string representing the three-letter day-of-week name (e.g., "Mon", "Tue", "Wed", etc.).
+#[derive(Debug)]
+pub struct DayNameFunc {
+    signature: Signature,
+}
+
+impl Default for DayNameFunc {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl DayNameFunc {
+    #[must_use]
+    pub fn new() -> Self {
+        Self {
+            signature: Signature::one_of(
+                vec![
+                    Coercible(vec![Coercion::new_exact(TypeSignatureClass::Timestamp)]),
+                    Exact(vec![DataType::Date32]),
+                    Exact(vec![DataType::Date64]),
+                ],
+                Volatility::Immutable,
+            ),
+        }
+    }
+}
+
+impl ScalarUDFImpl for DayNameFunc {
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+
+    fn name(&self) -> &'static str {
+        "dayname"
+    }
+
+    fn signature(&self) -> &Signature {
+        &self.signature
+    }
+
+    fn return_type(&self, _arg_types: &[DataType]) -> DFResult<DataType> {
+        Ok(DataType::Utf8)
+    }
+
+    #[allow(
+        clippy::unwrap_used,
+        clippy::as_conversions,
+        clippy::cast_possible_truncation
+    )]
+    fn invoke_with_args(&self, args: ScalarFunctionArgs) -> DFResult<ColumnarValue> {
+        let ScalarFunctionArgs { args, .. } = args;
+
+        let arr = match args[0].clone() {
+            ColumnarValue::Array(arr) => arr,
+            ColumnarValue::Scalar(v) => v.to_array()?,
+        };
+
+        let mut res = StringBuilder::with_capacity(arr.len(), 1024);
+        for i in 0..arr.len() {
+            let v = ScalarValue::try_from_array(&arr, i)?
+                .cast_to(&DataType::Timestamp(TimeUnit::Nanosecond, None))?;
+            let ScalarValue::TimestampNanosecond(Some(ts), None) = v else {
+                return exec_err!("First argument must be a timestamp with nanosecond precision");
+            };
+            let naive = DateTime::<Utc>::from_timestamp_nanos(ts).naive_utc();
+            res.append_value(dayname(&naive));
+        }
+
+        let res = res.finish();
+        Ok(if res.len() == 1 {
+            ColumnarValue::Scalar(ScalarValue::try_from_array(&res, 0)?)
+        } else {
+            ColumnarValue::Array(Arc::new(res))
+        })
+    }
+}
+
+fn dayname(date: &NaiveDateTime) -> String {
+    match date.weekday() {
+        chrono::Weekday::Mon => "Mon".to_string(),
+        chrono::Weekday::Tue => "Tue".to_string(),
+        chrono::Weekday::Wed => "Wed".to_string(),
+        chrono::Weekday::Thu => "Thu".to_string(),
+        chrono::Weekday::Fri => "Fri".to_string(),
+        chrono::Weekday::Sat => "Sat".to_string(),
+        chrono::Weekday::Sun => "Sun".to_string(),
+    }
+}
+
+crate::macros::make_udf_function!(DayNameFunc);
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use datafusion::prelude::SessionContext;
+    use datafusion_common::assert_batches_eq;
+    use datafusion_expr::ScalarUDF;
+
+    #[tokio::test]
+    async fn test_basic() -> DFResult<()> {
+        let ctx = SessionContext::new();
+        ctx.register_udf(ScalarUDF::from(DayNameFunc::new()));
+
+        let sql = "SELECT dayname('2025-05-08T23:39:20.123-07:00'::date) AS value;";
+        let result = ctx.sql(sql).await?.collect().await?;
+
+        assert_batches_eq!(
+            &[
+                "+-------+",
+                "| value |",
+                "+-------+",
+                "| Fri   |",
+                "+-------+",
+            ],
+            &result
+        );
+
+        Ok(())
+    }
+}

crates/embucket-functions/src/datetime/mod.rs

@@ -3,6 +3,7 @@ pub mod convert_timezone;
 pub mod date_add;
 pub mod date_diff;
 pub mod date_from_parts;
+pub mod dayname;
 pub mod last_day;
 pub mod next_day;
 pub mod previous_day;

crates/embucket-functions/src/datetime/previous_day.rs

@@ -114,7 +114,7 @@ impl ScalarUDFImpl for PreviousDayFunc {
 fn prev_day(ndt: &NaiveDateTime, dow: &str) -> DFResult<NaiveDateTime> {
     let target_dow = match dow.chars().take(2).collect::<String>().as_str() {
         "mo" => Weekday::Mon,
-        "tu" => Weekday::Thu,
+        "tu" => Weekday::Tue,
         "we" => Weekday::Wed,
         "th" => Weekday::Thu,
         "fr" => Weekday::Fri,

crates/embucket-functions/src/lib.rs

@@ -42,6 +42,7 @@ pub fn register_udfs(registry: &mut dyn FunctionRegistry) -> Result<()> {
         datetime::date_from_parts::get_udf(),
         datetime::last_day::get_udf(),
         datetime::add_months::get_udf(),
+        datetime::dayname::get_udf(),
         datetime::previous_day::get_udf(),
         datetime::next_day::get_udf(),
         conditional::booland::get_udf(),

crates/embucket-functions/src/visitors/unimplemented/generated_snowflake_functions.rs

@@ -841,12 +841,6 @@ pub const DATETIME_FUNCTIONS: &[(&str, FunctionInfo)] = &[
     )
     .with_docs("https://docs.snowflake.com/en/sql-reference/functions/year")
     ),
-    ("DAYNAME", FunctionInfo::new(
-        "DAYNAME",
-        "Extracts the three-letter day-of-week name from the specified date or timestamp."
-    )
-    .with_docs("https://docs.snowflake.com/en/sql-reference/functions/dayname")
-    ),
     ("DAYOFMONTH", FunctionInfo::new(
         "DAYOFMONTH",
         "Extracts the corresponding date part from a date or timestamp."

crates/embucket-functions/src/visitors/unimplemented/helper/implemented_functions.csv

@@ -130,7 +130,8 @@ dateadd
 datediff                           
 datefromparts                      
 datepart                           
-datetrunc                          
+datetrunc
+dayname
 decode                             
 degrees                            
 dense_rank