feat: support Utf8View type in starts_with function (#11787)

* feat: support `Utf8View` for `starts_with`

* style: clippy

* simplify string view handling

* fix: allow utf8 and largeutf8 to be cast into utf8view

* fix: fix test

* Apply suggestions from code review

Co-authored-by: Yongting You <[email protected]>
Co-authored-by: Andrew Lamb <[email protected]>

* style: fix format

* feat: add addiontal tests

* tests: improve tests

* fix: fix null case

* tests: one more null test

* Test comments and execution tests

---------

Co-authored-by: Yongting You <[email protected]>
Co-authored-by: Andrew Lamb <[email protected]>

Author: 3 people

datafusion/expr/src/expr_schema.rs

@@ -148,6 +148,7 @@ impl ExprSchemable for Expr {
                     .iter()
                     .map(|e| e.get_type(schema))
                     .collect::<Result<Vec<_>>>()?;
+
                 // verify that function is invoked with correct number and type of arguments as defined in `TypeSignature`
                 data_types_with_scalar_udf(&arg_data_types, func).map_err(|err| {
                     plan_datafusion_err!(

datafusion/expr/src/type_coercion/functions.rs

@@ -583,6 +583,10 @@ fn coerced_from<'a>(
         (Interval(_), _) if matches!(type_from, Utf8 | LargeUtf8) => {
             Some(type_into.clone())
         }
+        // We can go into a Utf8View from a Utf8 or LargeUtf8
+        (Utf8View, _) if matches!(type_from, Utf8 | LargeUtf8 | Null) => {
+            Some(type_into.clone())
+        }
         // Any type can be coerced into strings
         (Utf8 | LargeUtf8, _) => Some(type_into.clone()),
         (Null, _) if can_cast_types(type_from, type_into) => Some(type_into.clone()),
@@ -646,6 +650,18 @@ mod tests {
     use super::*;
     use arrow::datatypes::Field;
 
+    #[test]
+    fn test_string_conversion() {
+        let cases = vec![
+            (DataType::Utf8View, DataType::Utf8, true),
+            (DataType::Utf8View, DataType::LargeUtf8, true),
+        ];
+
+        for case in cases {
+            assert_eq!(can_coerce_from(&case.0, &case.1), case.2);
+        }
+    }
+
     #[test]
     fn test_maybe_data_types() {
         // this vec contains: arg1, arg2, expected result

datafusion/functions/src/string/starts_with.rs

@@ -18,10 +18,10 @@
 use std::any::Any;
 use std::sync::Arc;
 
-use arrow::array::{ArrayRef, OffsetSizeTrait};
+use arrow::array::ArrayRef;
 use arrow::datatypes::DataType;
 
-use datafusion_common::{cast::as_generic_string_array, internal_err, Result};
+use datafusion_common::{internal_err, Result};
 use datafusion_expr::ColumnarValue;
 use datafusion_expr::TypeSignature::*;
 use datafusion_expr::{ScalarUDFImpl, Signature, Volatility};
@@ -30,12 +30,8 @@ use crate::utils::make_scalar_function;
 
 /// Returns true if string starts with prefix.
 /// starts_with('alphabet', 'alph') = 't'
-pub fn starts_with<T: OffsetSizeTrait>(args: &[ArrayRef]) -> Result<ArrayRef> {
-    let left = as_generic_string_array::<T>(&args[0])?;
-    let right = as_generic_string_array::<T>(&args[1])?;
-
-    let result = arrow::compute::kernels::comparison::starts_with(left, right)?;
-
+pub fn starts_with(args: &[ArrayRef]) -> Result<ArrayRef> {
+    let result = arrow::compute::kernels::comparison::starts_with(&args[0], &args[1])?;
     Ok(Arc::new(result) as ArrayRef)
 }
 
@@ -52,14 +48,15 @@ impl Default for StartsWithFunc {
 
 impl StartsWithFunc {
     pub fn new() -> Self {
-        use DataType::*;
         Self {
             signature: Signature::one_of(
                 vec![
-                    Exact(vec![Utf8, Utf8]),
-                    Exact(vec![Utf8, LargeUtf8]),
-                    Exact(vec![LargeUtf8, Utf8]),
-                    Exact(vec![LargeUtf8, LargeUtf8]),
+                    // Planner attempts coercion to the target type starting with the most preferred candidate.
+                    // For example, given input `(Utf8View, Utf8)`, it first tries coercing to `(Utf8View, Utf8View)`.
+                    // If that fails, it proceeds to `(Utf8, Utf8)`.
+                    Exact(vec![DataType::Utf8View, DataType::Utf8View]),
+                    Exact(vec![DataType::Utf8, DataType::Utf8]),
+                    Exact(vec![DataType::LargeUtf8, DataType::LargeUtf8]),
                 ],
                 Volatility::Immutable,
             ),
@@ -81,18 +78,73 @@ impl ScalarUDFImpl for StartsWithFunc {
     }
 
     fn return_type(&self, _arg_types: &[DataType]) -> Result<DataType> {
-        use DataType::*;
-
-        Ok(Boolean)
+        Ok(DataType::Boolean)
     }
 
     fn invoke(&self, args: &[ColumnarValue]) -> Result<ColumnarValue> {
         match args[0].data_type() {
-            DataType::Utf8 => make_scalar_function(starts_with::<i32>, vec![])(args),
-            DataType::LargeUtf8 => {
-                return make_scalar_function(starts_with::<i64>, vec![])(args);
+            DataType::Utf8View | DataType::Utf8 | DataType::LargeUtf8 => {
+                make_scalar_function(starts_with, vec![])(args)
             }
-            _ => internal_err!("Unsupported data type"),
+            _ => internal_err!("Unsupported data types for starts_with. Expected Utf8, LargeUtf8 or Utf8View")?,
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::utils::test::test_function;
+    use arrow::array::{Array, BooleanArray};
+    use arrow::datatypes::DataType::Boolean;
+    use datafusion_common::{Result, ScalarValue};
+    use datafusion_expr::{ColumnarValue, ScalarUDFImpl};
+
+    use super::*;
+
+    #[test]
+    fn test_functions() -> Result<()> {
+        // Generate test cases for starts_with
+        let test_cases = vec![
+            (Some("alphabet"), Some("alph"), Some(true)),
+            (Some("alphabet"), Some("bet"), Some(false)),
+            (
+                Some("somewhat large string"),
+                Some("somewhat large"),
+                Some(true),
+            ),
+            (Some("somewhat large string"), Some("large"), Some(false)),
+        ]
+        .into_iter()
+        .flat_map(|(a, b, c)| {
+            let utf_8_args = vec![
+                ColumnarValue::Scalar(ScalarValue::Utf8(a.map(|s| s.to_string()))),
+                ColumnarValue::Scalar(ScalarValue::Utf8(b.map(|s| s.to_string()))),
+            ];
+
+            let large_utf_8_args = vec![
+                ColumnarValue::Scalar(ScalarValue::LargeUtf8(a.map(|s| s.to_string()))),
+                ColumnarValue::Scalar(ScalarValue::LargeUtf8(b.map(|s| s.to_string()))),
+            ];
+
+            let utf_8_view_args = vec![
+                ColumnarValue::Scalar(ScalarValue::Utf8View(a.map(|s| s.to_string()))),
+                ColumnarValue::Scalar(ScalarValue::Utf8View(b.map(|s| s.to_string()))),
+            ];
+
+            vec![(utf_8_args, c), (large_utf_8_args, c), (utf_8_view_args, c)]
+        });
+
+        for (args, expected) in test_cases {
+            test_function!(
+                StartsWithFunc::new(),
+                &args,
+                Ok(expected),
+                bool,
+                Boolean,
+                BooleanArray
+            );
+        }
+
+        Ok(())
+    }
+}

datafusion/sqllogictest/test_files/string_view.slt

@@ -355,6 +355,75 @@ logical_plan
 01)Aggregate: groupBy=[[]], aggr=[[count(DISTINCT test.column1_utf8), count(DISTINCT test.column1_utf8view), count(DISTINCT test.column1_dict)]]
 02)--TableScan: test projection=[column1_utf8, column1_utf8view, column1_dict]
 
+### `STARTS_WITH`
+
+# Test STARTS_WITH with utf8view against utf8view, utf8, and largeutf8
+# (should be no casts)
+query TT
+EXPLAIN SELECT
+  STARTS_WITH(column1_utf8view, column2_utf8view) as c1,
+  STARTS_WITH(column1_utf8view, column2_utf8) as c2,
+  STARTS_WITH(column1_utf8view, column2_large_utf8) as c3
+FROM test;
+----
+logical_plan
+01)Projection: starts_with(test.column1_utf8view, test.column2_utf8view) AS c1, starts_with(test.column1_utf8view, CAST(test.column2_utf8 AS Utf8View)) AS c2, starts_with(test.column1_utf8view, CAST(test.column2_large_utf8 AS Utf8View)) AS c3
+02)--TableScan: test projection=[column2_utf8, column2_large_utf8, column1_utf8view, column2_utf8view]
+
+query BBB
+SELECT
+  STARTS_WITH(column1_utf8view, column2_utf8view) as c1,
+  STARTS_WITH(column1_utf8view, column2_utf8) as c2,
+  STARTS_WITH(column1_utf8view, column2_large_utf8) as c3
+FROM test;
+----
+false false false
+true true true
+true true true
+NULL NULL NULL
+
+# Test STARTS_WITH with utf8 against utf8view, utf8, and largeutf8
+# Should work, but will have to cast to common types
+# should cast utf8 -> utf8view and largeutf8 -> utf8view
+query TT
+EXPLAIN SELECT
+  STARTS_WITH(column1_utf8, column2_utf8view) as c1,
+  STARTS_WITH(column1_utf8, column2_utf8) as c3,
+  STARTS_WITH(column1_utf8, column2_large_utf8) as c4
+FROM test;
+----
+logical_plan
+01)Projection: starts_with(__common_expr_1, test.column2_utf8view) AS c1, starts_with(test.column1_utf8, test.column2_utf8) AS c3, starts_with(__common_expr_1, CAST(test.column2_large_utf8 AS Utf8View)) AS c4
+02)--Projection: CAST(test.column1_utf8 AS Utf8View) AS __common_expr_1, test.column1_utf8, test.column2_utf8, test.column2_large_utf8, test.column2_utf8view
+03)----TableScan: test projection=[column1_utf8, column2_utf8, column2_large_utf8, column2_utf8view]
+
+query BBB
+ SELECT
+  STARTS_WITH(column1_utf8, column2_utf8view) as c1,
+  STARTS_WITH(column1_utf8, column2_utf8) as c3,
+  STARTS_WITH(column1_utf8, column2_large_utf8) as c4
+FROM test;
+----
+false false false
+true true true
+true true true
+NULL NULL NULL
+
+
+# Test STARTS_WITH with utf8view against literals
+# In this case, the literals should be cast to utf8view. The columns
+# should not be cast to utf8.
+query TT
+EXPLAIN SELECT
+  STARTS_WITH(column1_utf8view, 'äöüß') as c1,
+  STARTS_WITH(column1_utf8view, '') as c2,
+  STARTS_WITH(column1_utf8view, NULL) as c3,
+  STARTS_WITH(NULL, column1_utf8view) as c4
+FROM test;
+----
+logical_plan
+01)Projection: starts_with(test.column1_utf8view, Utf8View("äöüß")) AS c1, starts_with(test.column1_utf8view, Utf8View("")) AS c2, starts_with(test.column1_utf8view, Utf8View(NULL)) AS c3, starts_with(Utf8View(NULL), test.column1_utf8view) AS c4
+02)--TableScan: test projection=[column1_utf8view]
 
 statement ok
 drop table test;
@@ -376,6 +445,5 @@ select t.dt from dates t where arrow_cast('2024-01-01', 'Utf8View') < t.dt;
 ----
 2024-01-23
 
-
 statement ok
 drop table dates;