support scientific notation big floats

[yungtrizzle]

Adds some support following discovery of #1758 by

1. detecting scientific notation
2. scan into big/Float
3. replace original string with a true numeric string
4. ensure using minimal significant figures after the decimal

[jackc]

Does PostgreSQL ever return numerics in scientific notation? If not, I'm not sure that Scan is the right place for that logic.

[yungtrizzle]

Does PostgreSQL ever return numerics in scientific notation? If not, I'm not sure that Scan is the right place for that logic.

Not necessarily but Scan is the only method to instantiate a numeric when it's not a returned value from a query. This is a common case for sending numerics to PostgreSQL

[jackc]

Would it make sense to instead add a ScanScientific or something like that? It seems slightly off to me to make a function whose purpose is to scan values PostgreSQL produces also do something else. Numeric already has a couple Scan* methods so it wouldn't be unprecedented.

Also, I'm a little surprised that Numeric is being used directly. It is included so pgx can represent numeric values without an external dependency, but I expected anyone who was actually using PostgreSQL numerics would use something like https://github.com/shopspring/decimal.

[yungtrizzle]

I'm okay with making it a separate function, didn't realize the others were public. Let me push that update.

I expected anyone who was actually using PostgreSQL numerics would use something like https://github.com/shopspring/decimal.

In many cases, there isn't a need for all that it provides. In our case at $WORK, we only need to represent big numbers, no math needed so pulling it in is like using a sledgehammer to crack a nut. We've found that math/big + pgx is quite robust