feat: support decimals in trunc UDF

datafusion/functions/src/math/trunc.rs

@@ -15,22 +15,32 @@
 // specific language governing permissions and limitations
 // under the License.
 
+use std::ops::{Div, Mul};
 use std::sync::Arc;
 
-use crate::utils::make_scalar_function;
+use crate::utils::{calculate_binary_decimal_math_cast, make_scalar_function};
 
 use arrow::array::{ArrayRef, AsArray, PrimitiveArray};
-use arrow::datatypes::DataType::{Float32, Float64};
-use arrow::datatypes::{DataType, Float32Type, Float64Type, Int64Type};
+use arrow::datatypes::DataType::{
+    Decimal32, Decimal64, Decimal128, Decimal256, Float32, Float64,
+};
+use arrow::datatypes::{
+    DataType, Decimal32Type, Decimal64Type, Decimal128Type, Decimal256Type, DecimalType,
+    Float32Type, Float64Type, Int64Type,
+};
 use datafusion_common::ScalarValue::Int64;
-use datafusion_common::{Result, ScalarValue, exec_err};
-use datafusion_expr::TypeSignature::Exact;
+use datafusion_common::types::{
+    NativeType, logical_float32, logical_float64, logical_int64,
+};
+use datafusion_common::{Result, ScalarValue, exec_err, plan_err};
 use datafusion_expr::sort_properties::{ExprProperties, SortProperties};
 use datafusion_expr::{
     ColumnarValue, Documentation, ScalarFunctionArgs, ScalarUDFImpl, Signature,
     Volatility,
 };
+use datafusion_expr_common::signature::{Coercion, TypeSignature, TypeSignatureClass};
 use datafusion_macros::user_doc;
+use num_traits::{One, Zero, pow};
 
 #[user_doc(
     doc_section(label = "Math Functions"),
@@ -68,19 +78,38 @@ impl Default for TruncFunc {
 
 impl TruncFunc {
     pub fn new() -> Self {
-        use DataType::*;
+        let decimal = Coercion::new_exact(TypeSignatureClass::Decimal);
+        let decimal_places = Coercion::new_implicit(
+            TypeSignatureClass::Native(logical_int64()),
+            vec![TypeSignatureClass::Integer],
+            NativeType::Int64,
+        );
+        let float32 = Coercion::new_exact(TypeSignatureClass::Native(logical_float32()));
+        let float64 = Coercion::new_implicit(
+            TypeSignatureClass::Native(logical_float64()),
+            vec![TypeSignatureClass::Numeric],
+            NativeType::Float64,
+        );
         Self {
             // math expressions expect 1 argument of type f64 or f32
             // priority is given to f64 because e.g. `sqrt(1i32)` is in IR (real numbers) and thus we
             // return the best approximation for it (in f64).
             // We accept f32 because in this case it is clear that the best approximation
-            // will be as good as the number of digits in the number
+            // Decimal arguments are accepted to handle large values properly
             signature: Signature::one_of(
                 vec![
-                    Exact(vec![Float32, Int64]),
-                    Exact(vec![Float64, Int64]),
-                    Exact(vec![Float64]),
-                    Exact(vec![Float32]),
+                    TypeSignature::Coercible(vec![
+                        decimal.clone(),
+                        decimal_places.clone(),
+                    ]),
+                    TypeSignature::Coercible(vec![decimal]),
+                    TypeSignature::Coercible(vec![
+                        float32.clone(),
+                        decimal_places.clone(),
+                    ]),
+                    TypeSignature::Coercible(vec![float32]),
+                    TypeSignature::Coercible(vec![float64.clone(), decimal_places]),
+                    TypeSignature::Coercible(vec![float64]),
                 ],
                 Volatility::Immutable,
             ),
@@ -98,9 +127,16 @@ impl ScalarUDFImpl for TruncFunc {
     }
 
     fn return_type(&self, arg_types: &[DataType]) -> Result<DataType> {
-        match arg_types[0] {
+        match &arg_types[0] {
             Float32 => Ok(Float32),
-            _ => Ok(Float64),
+            Float64 => Ok(Float64),
+            dt if dt.is_decimal() => Ok(dt.clone()),
+            DataType::Null => Ok(Float64),
+            _ => plan_err!(
+                "Unsupported data type {:?} for function {}",
+                arg_types[0],
+                self.name()
+            ),
         }
     }
 
@@ -146,6 +182,55 @@ impl ScalarUDFImpl for TruncFunc {
                     compute_truncate32(*v, p)
                 }))),
             ),
+            (
+                ColumnarValue::Scalar(ScalarValue::Decimal32(
+                    Some(v),
+                    lprecision,
+                    lscale,
+                )),
+                Some(p),
+            ) => Ok(ColumnarValue::Scalar(ScalarValue::Decimal32(
+                Some(compute_truncate_decimal::<Decimal32Type>(*v, *lscale, p)),
+                *lprecision,
+                *lscale,
+            ))),
+            (
+                ColumnarValue::Scalar(ScalarValue::Decimal64(
+                    Some(v),
+                    lprecision,
+                    lscale,
+                )),
+                Some(p),
+            ) => Ok(ColumnarValue::Scalar(ScalarValue::Decimal64(
+                Some(compute_truncate_decimal::<Decimal64Type>(*v, *lscale, p)),
+                *lprecision,
+                *lscale,
+            ))),
+            (
+                ColumnarValue::Scalar(ScalarValue::Decimal128(
+                    Some(v),
+                    lprecision,
+                    lscale,
+                )),
+                Some(p),
+            ) => Ok(ColumnarValue::Scalar(ScalarValue::Decimal128(
+                Some(compute_truncate_decimal::<Decimal128Type>(*v, *lscale, p)),
+                *lprecision,
+                *lscale,
+            ))),
+            (
+                ColumnarValue::Scalar(ScalarValue::Decimal256(
+                    Some(v),
+                    lprecision,
+                    lscale,
+                )),
+                Some(p),
+            ) => Ok(ColumnarValue::Scalar(ScalarValue::Decimal256(
+                Some(compute_truncate_decimal::<Decimal256Type>(*v, *lscale, p)),
+                *lprecision,
+                *lscale,
+            ))),
+
             // Array path for everything else
             _ => make_scalar_function(trunc, vec![])(&args.args),
         }
@@ -234,6 +319,58 @@ fn trunc(args: &[ArrayRef]) -> Result<ArrayRef> {
             }
             _ => exec_err!("trunc function requires a scalar or array for precision"),
         },
+        Decimal32(lprecision, lscale) => Ok(calculate_binary_decimal_math_cast::<
+            Decimal32Type,
+            Int64Type,
+            Decimal32Type,
+            _,
+        >(
+            num.as_ref(),
+            &precision,
+            |v, y| Ok(compute_truncate_decimal::<Decimal32Type>(v, *lscale, y)),
+            *lprecision,
+            *lscale,
+            &DataType::Int64,
+        )? as ArrayRef),
+        Decimal64(lprecision, lscale) => Ok(calculate_binary_decimal_math_cast::<
+            Decimal64Type,
+            Int64Type,
+            Decimal64Type,
+            _,
+        >(
+            num.as_ref(),
+            &precision,
+            |v, y| Ok(compute_truncate_decimal::<Decimal64Type>(v, *lscale, y)),
+            *lprecision,
+            *lscale,
+            &DataType::Int64,
+        )? as ArrayRef),
+        Decimal128(lprecision, lscale) => Ok(calculate_binary_decimal_math_cast::<
+            Decimal128Type,
+            Int64Type,
+            Decimal128Type,
+            _,
+        >(
+            num.as_ref(),
+            &precision,
+            |v, y| Ok(compute_truncate_decimal::<Decimal128Type>(v, *lscale, y)),
+            *lprecision,
+            *lscale,
+            &DataType::Int64,
+        )? as ArrayRef),
+        Decimal256(lprecision, lscale) => Ok(calculate_binary_decimal_math_cast::<
+            Decimal256Type,
+            Int64Type,
+            Decimal256Type,
+            _,
+        >(
+            num.as_ref(),
+            &precision,
+            |v, y| Ok(compute_truncate_decimal::<Decimal256Type>(v, *lscale, y)),
+            *lprecision,
+            *lscale,
+            &DataType::Int64,
+        )? as ArrayRef),
         other => exec_err!("Unsupported data type {other:?} for function trunc"),
     }
 }
@@ -248,13 +385,52 @@ fn compute_truncate64(x: f64, y: i64) -> f64 {
     (x * factor).trunc() / factor
 }
 
+/// Truncates a decimal value to `truncate_precision` fractional digits.
+/// If `truncate_precision` is positive, clear that amount of trailing low-order digits
+/// If `truncate_precision` is negative, it also clears digits before a decimal point
+///
+/// Example:
+///   Truncating number 12.3456 (123456 as i128 with scale=4) to 1 digit produces 12.3.
+///   It makes exp = 4-1 = 3; factor = 10^3 = 1000; result = (123456 / 1000) * 1000 = 123000
+///   It is a decimal 12.3 with scale=4
+///
+///   Truncating number 12.3456 to -1 digit produces 10.0.
+///   It makes exp = 4-(-1) = 5; factor = 10^5 = 100000; result = (123456 / 100000) * 100000 = 100000
+///   It is a decimal 10.0 with scale=4
+fn compute_truncate_decimal<T>(
+    x: T::Native,
+    scale: i8,
+    truncate_precision: i64,
+) -> T::Native
+where
+    T: DecimalType,
+    T::Native: Copy + From<i32> + One + Zero + Div<Output = T::Native> + Mul,
+{
+    // How many trailing digits of decimal to clear
+    let exp = (scale as i64).saturating_sub(truncate_precision);
+    if exp <= 0 {
+        // Keep more digits than actually stored, so nothing to truncate
+        x
+    } else if exp >= T::MAX_PRECISION as i64 {
+        // Drop more digits that can be stored, return 0 without overflowing `pow`
+        T::Native::zero()
+    } else {
+        let base = T::Native::from(10_i32);
+        let exp = exp as usize;
+        let factor = pow::<T::Native>(base, exp);
+        // Result is (x / factor) * factor, so (x/factor) drops extra digits
+        (x / factor) * factor
+    }
+}
+
 #[cfg(test)]
 mod test {
     use std::sync::Arc;
 
-    use crate::math::trunc::trunc;
+    use crate::math::trunc::{compute_truncate_decimal, trunc};
 
     use arrow::array::{ArrayRef, Float32Array, Float64Array, Int64Array};
+    use arrow::datatypes::Decimal128Type;
     use datafusion_common::cast::{as_float32_array, as_float64_array};
 
     #[test]
@@ -328,4 +504,60 @@ mod test {
         assert_eq!(floats.value(3), 123.0);
         assert_eq!(floats.value(4), -321.0);
     }
+
+    #[test]
+    fn test_compute_truncate_decimal128() {
+        // number 12.3456 (scale 4) truncated to 3 places = 12.345
+        assert_eq!(
+            compute_truncate_decimal::<Decimal128Type>(123_456, 4, 3),
+            123_450
+        );
+        // number 12.3456 (scale 4) truncated to 1 place = 12.3
+        assert_eq!(
+            compute_truncate_decimal::<Decimal128Type>(123_456, 4, 1),
+            123_000
+        );
+
+        // requesting more places = no change
+        assert_eq!(
+            compute_truncate_decimal::<Decimal128Type>(123_456, 4, 10),
+            123_456
+        );
+
+        // truncating to 0 places = whole number 12
+        assert_eq!(
+            compute_truncate_decimal::<Decimal128Type>(123_456, 4, 0),
+            120_000
+        );
+
+        // number 12.3456 (scale 2) truncated to -1 places = 10
+        assert_eq!(
+            compute_truncate_decimal::<Decimal128Type>(123_456, 4, -1),
+            100_000
+        );
+
+        // number 12.3456 (scale 2) truncated to -3 places = 0
+        assert_eq!(
+            compute_truncate_decimal::<Decimal128Type>(123_456, 4, -3),
+            0
+        );
+
+        // number 1234.56 (scale 2) truncated to -3 places = 1000
+        assert_eq!(
+            compute_truncate_decimal::<Decimal128Type>(123_456, 2, -3),
+            100_000
+        );
+
+        // out of scale
+        assert_eq!(
+            compute_truncate_decimal::<Decimal128Type>(123_456, 4, -900),
+            0
+        );
+
+        // truncation rounds towards zero: -12.3456 = -12.345
+        assert_eq!(
+            compute_truncate_decimal::<Decimal128Type>(-123_456, 4, 3),
+            -123_450
+        );
+    }
 }

datafusion/sqllogictest/test_files/scalar.slt

@@ -1333,6 +1333,57 @@ from small_floats;
 0.836 0.8 0.836
 1 1 1
 
+# trunc with decimals
+query RT
+select trunc(arrow_cast(3.1415, 'Decimal128(10,4)')), arrow_typeof(trunc(arrow_cast(3.1415, 'Decimal128(10,4)')));
+----
+3 Decimal128(10, 4)
+
+# trunc with precision - decimals
+query RRRRR rowsort
+select
+  trunc(arrow_cast(4.267, 'Decimal32(8,3)'), 3),
+  trunc(arrow_cast(1.1234, 'Decimal64(18,6)'), 2),
+  trunc(arrow_cast(-1.1231, 'Decimal128(15,4)'), 6),
+  trunc(arrow_cast(1.2837284, 'Decimal256(35,7)'), 2),
+  trunc(arrow_cast(1.1, 'Decimal128(10,1)'), 0);
+----
+4.267 1.12 -1.1231 1.28 1
+
+# trunc with negative precision should truncate digits left of decimal - decimal types
+query RT
+select trunc(arrow_cast(12345.678, 'Decimal128(10,3)'), -3),
+       arrow_typeof(trunc(arrow_cast(12345.678, 'Decimal128(10,3)'), -3));
+----
+12000 Decimal128(10, 3)
+
+# trunc: coercion with a decimal argument and a non-int64 precision argument
+query RT
+select trunc(arrow_cast(1.2345678, 'Decimal128(20,14)'), arrow_cast(2, 'Int32')),
+       arrow_typeof(trunc(arrow_cast(1.2345678, 'Decimal128(20,14)'), arrow_cast(2, 'Int32')));
+----
+1.23 Decimal128(20, 14)
+
+# trunc with columns and precision - decimal128
+query RRR rowsort
+select
+  trunc(arrow_cast(a, 'Decimal128(10,4)'), 0) as a0,
+  trunc(arrow_cast(b, 'Decimal128(10,4)'), 0) as b0,
+  trunc(arrow_cast(c, 'Decimal128(10,4)'), 0) as c0
+from small_floats;
+----
+-1 NULL NULL
+0 0 -1
+0 0 0
+0 0 1
+
+# trunc issue #22512
+query R
+select trunc(CAST(9007199254740993 AS DECIMAL(20,0)));
+----
+9007199254740993
+
+
 ## bitwise and
 
 # bitwise and with column and scalar