Weijun-H commented on code in PR #21322: URL: https://github.com/apache/datafusion/pull/21322#discussion_r3035640528
########## datafusion/functions/src/core/cast_to_type.rs: ########## @@ -0,0 +1,147 @@ +// 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. + +//! [`CastToTypeFunc`]: Implementation of the `cast_to_type` + +use arrow::datatypes::{DataType, Field, FieldRef}; +use datafusion_common::{ + Result, datatype::DataTypeExt, internal_err, utils::take_function_args, +}; +use datafusion_expr::simplify::{ExprSimplifyResult, SimplifyContext}; +use datafusion_expr::{ + Coercion, ColumnarValue, Documentation, Expr, ReturnFieldArgs, ScalarFunctionArgs, + ScalarUDFImpl, Signature, TypeSignatureClass, Volatility, +}; +use datafusion_macros::user_doc; + +/// Casts the first argument to the data type of the second argument. +/// +/// Only the type of the second argument is used; its value is ignored. +/// This is useful in macros or generic SQL where you need to preserve +/// or match types dynamically. +/// +/// For example: +/// ```sql +/// select cast_to_type('42', NULL::INTEGER); +/// ``` +#[user_doc( + doc_section(label = "Other Functions"), + description = "Casts the first argument to the data type of the second argument. Only the type of the second argument is used; its value is ignored.", + syntax_example = "cast_to_type(expression, reference)", + sql_example = r#"```sql +> select cast_to_type('42', NULL::INTEGER) as a; ++----+ +| a | ++----+ +| 42 | ++----+ + +> select cast_to_type(1 + 2, NULL::DOUBLE) as b; ++-----+ +| b | ++-----+ +| 3.0 | ++-----+ +```"#, + argument( + name = "expression", + description = "Expression to cast. The expression can be a constant, column, or function, and any combination of operators." + ), + argument( + name = "reference", + description = "Reference expression whose data type determines the target cast type. The value is ignored." + ) +)] +#[derive(Debug, PartialEq, Eq, Hash)] +pub struct CastToTypeFunc { + signature: Signature, +} + +impl Default for CastToTypeFunc { + fn default() -> Self { + Self::new() + } +} + +impl CastToTypeFunc { + pub fn new() -> Self { + Self { + signature: Signature::coercible( + vec![ + Coercion::new_exact(TypeSignatureClass::Any), + Coercion::new_exact(TypeSignatureClass::Any), + ], + Volatility::Immutable, + ), + } + } +} + +impl ScalarUDFImpl for CastToTypeFunc { + fn name(&self) -> &str { + "cast_to_type" + } + + fn signature(&self) -> &Signature { + &self.signature + } + + fn return_type(&self, _arg_types: &[DataType]) -> Result<DataType> { + internal_err!("return_field_from_args should be called instead") + } + + fn return_field_from_args(&self, args: ReturnFieldArgs) -> Result<FieldRef> { + let nullable = args.arg_fields.iter().any(|f| f.is_nullable()); Review Comment: This looks incorrect to me. `reference` is only used for its type, but its nullability is being propagated to the result schema. That means expressions like `cast_to_type(42, NULL::INTEGER)` become nullable in the logical plan schema. I think `cast_to_type` should only inherit nullability from the first argument? -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
