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Posted to github@arrow.apache.org by "alamb (via GitHub)" <gi...@apache.org> on 2023/02/02 22:11:04 UTC
[GitHub] [arrow-datafusion] alamb commented on a diff in pull request #5166: feat: add `arrow_cast` function to support supports arbitrary arrow types
alamb commented on code in PR #5166:
URL: https://github.com/apache/arrow-datafusion/pull/5166#discussion_r1095137824
##########
datafusion/core/tests/sqllogictests/test_files/arrow_typeof.slt:
##########
@@ -52,31 +52,78 @@ SELECT arrow_typeof(1.0::float)
Float32
# arrow_typeof_decimal
-# query T
-# SELECT arrow_typeof(1::Decimal)
-# ----
-# Decimal128(38, 10)
-
-# # arrow_typeof_timestamp
-# query T
-# SELECT arrow_typeof(now()::timestamp)
-# ----
-# Timestamp(Nanosecond, None)
-
-# # arrow_typeof_timestamp_utc
-# query T
-# SELECT arrow_typeof(now())
-# ----
-# Timestamp(Nanosecond, Some(\"+00:00\"))
-
-# # arrow_typeof_timestamp_date32(
-# query T
-# SELECT arrow_typeof(now()::date)
-# ----
-# Date32
-
-# # arrow_typeof_utf8
-# query T
-# SELECT arrow_typeof('1')
-# ----
-# Utf8
+query T
Review Comment:
I just uncommented out these tests -- I am not sure why they were commented out 🤷
##########
datafusion/sql/src/expr/function.rs:
##########
@@ -116,24 +118,29 @@ impl<'a, S: ContextProvider> SqlToRel<'a, S> {
};
// finally, user-defined functions (UDF) and UDAF
- match self.schema_provider.get_function_meta(&name) {
- Some(fm) => {
- let args = self.function_args_to_expr(function.args, schema)?;
+ if let Some(fm) = self.schema_provider.get_function_meta(&name) {
+ let args = self.function_args_to_expr(function.args, schema)?;
+ return Ok(Expr::ScalarUDF { fun: fm, args });
+ }
- Ok(Expr::ScalarUDF { fun: fm, args })
- }
- None => match self.schema_provider.get_aggregate_meta(&name) {
- Some(fm) => {
- let args = self.function_args_to_expr(function.args, schema)?;
- Ok(Expr::AggregateUDF {
- fun: fm,
- args,
- filter: None,
- })
- }
- _ => Err(DataFusionError::Plan(format!("Invalid function '{name}'"))),
- },
+ // User defined aggregate functions
+ if let Some(fm) = self.schema_provider.get_aggregate_meta(&name) {
+ let args = self.function_args_to_expr(function.args, schema)?;
+ return Ok(Expr::AggregateUDF {
+ fun: fm,
+ args,
+ filter: None,
+ });
}
+
+ // Special case arrow_cast
+ if &name == ARROW_CAST_NAME {
Review Comment:
This is the main difference -- if all other function resolution fails, try to resolve it as `arrow_cast` before erroring
##########
datafusion/sql/src/expr/function.rs:
##########
@@ -116,24 +118,29 @@ impl<'a, S: ContextProvider> SqlToRel<'a, S> {
};
// finally, user-defined functions (UDF) and UDAF
- match self.schema_provider.get_function_meta(&name) {
- Some(fm) => {
- let args = self.function_args_to_expr(function.args, schema)?;
+ if let Some(fm) = self.schema_provider.get_function_meta(&name) {
Review Comment:
This change was just to reduce the indent level (as adding support for `arrow_cast` in the existing structure would have added another level)
##########
datafusion/sql/src/expr/cast.rs:
##########
@@ -0,0 +1,100 @@
+// 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.
+
+//! Implementation of the `arrow_cast` function.
+
+use arrow_schema::DataType;
+use datafusion_common::{DFSchema, DataFusionError, Result, ScalarValue};
+
+use datafusion_expr::{Expr, ExprSchemable};
+
+pub const ARROW_CAST_NAME: &str = "arrow_cast";
+
+/// Create an Expr that evaluates the arrow cast function
+///
+/// This function is not a [`BuiltInScalarFunction`] because the
+/// return type of such a function depends only on the *types* of
+/// their input. However, the type of `arrow_type` depends on the
+/// *value* of its second argument
+///
+/// Use the `cast` function to cast to SQL type (which is then mapped
+/// to the corresponding arrow type). For example to cast to `int`
+/// (which is then mapped to the arrow type `Int32`)
+///
+/// ```sql
+/// select cast(column_x as int) ...
+/// ```
+///
+/// Use the `arrow_cast` functiont to cast to a specfic arrow type
+///
+/// For example
+/// ```sql
+/// select arrow_cast(column_x, 'Float64')
+/// ```
+pub fn create_arrow_cast(mut args: Vec<Expr>, schema: &DFSchema) -> Result<Expr> {
+ if args.len() != 2 {
+ return Err(DataFusionError::Plan(format!(
+ "arrow_cast needs 2 arguments, {} provided",
+ args.len()
+ )));
+ }
+ let arg1 = args.pop().unwrap();
+ let arg0 = args.pop().unwrap();
+
+ // arg1 must be a stirng
+ let data_type_string = if let Expr::Literal(ScalarValue::Utf8(Some(v))) = arg1 {
+ v
+ } else {
+ return Err(DataFusionError::Plan(format!(
+ "arrow_cast requires its second argument to be a constant string, got {arg1}"
+ )));
+ };
+
+ // do the actual lookup to the appropriate data type
+ let data_type = parse_data_type(&data_type_string)?;
+
+ return arg0.cast_to(&data_type, schema);
Review Comment:
the actual implementation simply calls the existing `Expr::Cast`
##########
datafusion/sql/tests/integration_test.rs:
##########
@@ -2497,7 +2506,7 @@ impl ContextProvider for MockContextProvider {
}
fn get_function_meta(&self, _name: &str) -> Option<Arc<ScalarUDF>> {
- unimplemented!()
+ None
Review Comment:
otherwise the test context panic's before it gets to seeing `arrow_cast`
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