[GitHub] [pinot] walterddr opened a new issue, #8610: [Feature] Support dynamic return type in function such as CAST

[GitBox <gi...@apache.org>]

walterddr opened a new issue, #8610:
URL: https://github.com/apache/pinot/issues/8610

   Background
   ===
   Following #8597 to support argument-type-based function lookup, it is possible that argument types themselves is not sufficient to determine the result type, for example `CAST(intCol AS 'long')` and `CAST(intCol AS 'int')` will have the same argument types `int, string` but different return type `long` vs. `int`.
   
   
   Proposal
   ===
   Propose to allow annotation of `@ScalarFunction` to annotate classes which have various function/method name, signature, class will look like this 
   ```
   @ScalarFunction(name = 'cast')
   public class CastFunction implements FunctionDefinition {
   
     @Override
     public Method getMethod(Collection<DataType> argumentType, Collection<Literal> literalArguments) {
       // ... 
     }
   
     // actual function methods:
     public int castToInt(Object o, String literalCastType) { // ... }
     public long castToLong(Object o , String literalCastType) { // ... }
   }
   ```
   Similar architecture is adopted in many sql-like systems to support UDF/UDAF/UDTF etc. thus I think the design should be sufficient. 
   
   
   Note
   ====
   * type inference is not discussed in this document
   * whether to use codegen or hand-written method is up for discussion.
   
   


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