Re: Add Roman numeral conversion to to_number

On Thursday, 3 August 2017, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:

> On Thu, Aug 3, 2017 at 9:25 AM, Oliver Ford <ojford(at)gmail(dot)com
> <javascript:;>> wrote:
> > Adds to the to_number() function the ability to convert Roman numerals
> > to a number. This feature is on the formatting.c TODO list. It is not
> > currently implemented in either Oracle, MSSQL or MySQL so gives
> > PostgreSQL an edge :-)
>
> I kind of put my head in my hands when I saw this. I'm not really
> sure it's worth complicating the code for something that has so little
> practical utility, but maybe other people will feel differently. I
> can't deny the profound advantages associated with having a leg up on
> Oracle.

The formatting.c file specifies it as a TODO, so I thought implementing it
would be worthwhile. As there is a to_roman conversion having it the other
way is good for completeness.

>
> The error reporting is a little wonky, although maybe no wonkier than
> anything else about these conversion routines.
>
> rhaas=# select to_number('q', 'rn');
> ERROR: invalid character "q"
>
> (hmm, no position)
>
> rhaas=# select to_number('dd', 'rn');
> ERROR: invalid character "D" at position 1
>
> (now i get a position, but it's not really the right position; and the
> problem isn't really that the character is invalid but that you don't
> like me including it twice, and I said 'd' not 'D')
>
> rhaas=# select to_number('à', 'rn');
> ERROR: invalid character "?"
>
> (eh?)
>
> How much call is there for a format that can only represent values up to
> 3999?
>
>
The existing int_to_roman code goes up to 3999 so this patch is consistent
with that. I could extend both to handle Unicode values for large numbers?

> --
> Robert Haas
> EnterpriseDB: http://www.enterprisedb.com
> The Enterprise PostgreSQL Company
>