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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