SQL: Add PARSE_LONG function.

[gianm]

Motivation

We have a need to treat hex and octal strings as integers at both ingest time (transformSpec) and query time. Currently, we can do this with decimals, but not with hex/octal.

Proposed changes

• Add a parse_long Druid expression function (see math-expr.md for docs)
• Add a PARSE_LONG Druid SQL function (see sql.md for docs)

Both functions have a required argument (string) and an optional argument (radix, defaults to 10 - decimal). Both functions return a long. Both functions return null if the string is not parseable.

Rationale

PARSE_LONG(x) acts the same as CAST(x AS BIGINT). Both treat x as decimal and return null if the string is not parseable. But PARSE_LONG is more flexible, since it can accept different radixes and parse hex, octal, etc. So this design was really chosen for alignment with behavior of CAST.

There doesn't seem to be a great way to do this in standard SQL, at least that I can find (see some hilariousness in https://stackoverflow.com/questions/8316164/convert-hex-in-text-representation-to-decimal-number). So I made up my own syntax and semantics. I chose PARSE_LONG for the name since it would be familiar to Java users.

Operational impact

None.

Test plan

Unit tests.