Proposed changes
1. function interfaces that can search the matched signature, say ComputeSignature. It's equal to the Function.CompareMode.
- IdenticalSignature: equal to Function.CompareMode.IS_IDENTICAL
- NullOrIdenticalSignature: equal to Function.CompareMode.IS_INDISTINGUISHABLE
- ImplicitlyCastableSignature: equal to Function.CompareMode.IS_SUPERTYPE_OF
- ExplicitlyCastableSignature: equal to Function.CompareMode.IS_NONSTRICT_SUPERTYPE_OF
3. generate lots of scalar functions
4. bug-fix: disassemble avg function compute wrong result because the wrong input type, the AggregateParam.inputTypesBeforeDissemble is use to save the origin input type and pass to backend to find the correct global aggregate function.
5. bug-fix: subquery with OneRowRelation will crash because wrong nullable property
Note:
1. currently no more unit test/regression test for the scalar functions, I will add the test until migrate aggregate functions for unified processing.
2. A known problem is can not invoke the variable length function, I will fix it later.
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