Add UDFs for String Transformation

[KKcorps]

Currently Pinot has UDF defined for all the math operators. The same needs to be done for string operators.

[SandishKumarHN]

@KKcorps was thinking to add the below string functions

1. string1 + string2 = Concatenates (joins) string1 and string2
2. string * x = Returns the characters from the range provided at x:y.
3. string[x:y] = Returns the characters from the range provided at x:y.
4. x in string = Returns True if x exists in the string. Can be multiple characters.
5. x not in string = Returns True if x does not exist in the string. Can be multiple characters.

is that what we are looking for?

[xiangfu0]

Just fyi, there are String functions already implemented: https://github.com/apache/incubator-pinot/blob/master/pinot-common/src/main/java/org/apache/pinot/common/function/scalar/StringFunctions.java

We can try to translate the operators to use those functions and adding missing functions.

[KKcorps]

@SandishKumarHN Functions for 1 and 3rd already exist. You can implement the rest in the class provided by @fx19880617

[SandishKumarHN]

@fx19880617 @KKcorps will add those string functions in StringFunctions class

[xiangfu0]

Closing — this has been implemented in PR #5440 (GenericTransformFunction wrapper for scalar functions) and PR #6458 (additional string scalar functions). UDFs for string transformation are now available.