Обсуждение: "format" function documentation fix

(Please CC me the reply, since I'm not subscribed to the list.)

Hi,

The last example from
http://www.postgresql.org/docs/9.3/static/functions-string.html#FUNCTIONS-STRING-FORMAT
- "examples using width fields and the - flag" seems to be incorrect,
see the attached patch.

Regards,

r.

On 14 September 2013 09:29, rudolf <stu3.1@eq.cz> wrote:
> (Please CC me the reply, since I'm not subscribed to the list.)
>
> Hi,
>
> The last example from
> http://www.postgresql.org/docs/9.3/static/functions-string.html#FUNCTIONS-STRING-FORMAT
> - "examples using width fields and the - flag" seems to be incorrect, see
> the attached patch.
>

No, the example is correct. Referring to the documentation above that:

    If the width argument is negative, the result is left aligned (as
if the - flag had been specified) ...

This applies even if the "-" flag is also specified. So the last
example is meant to illustrate that 2 minuses don't make a plus here.

Regards,
Dean

On 17 September 2013 10:00, rudolf <stu3.1@eq.cz> wrote:
> (Please CC me the reply, since I'm not subscribed to the list.)
>
> Dean Rasheed wrote:
>>
>> On 14 September 2013 09:29, rudolf <stu3.1@eq.cz> wrote:
>>>
>>> The last example from
>>>
>>> http://www.postgresql.org/docs/9.3/static/functions-string.html#FUNCTIONS-STRING-FORMAT
>>> - "examples using width fields and the - flag" seems to be incorrect, see
>>> the attached patch.
>>
>>
>> No, the example is correct. Referring to the documentation above that:
>>
>>      If the width argument is negative, the result is left aligned (as
>> if the - flag had been specified) ...
>>
>> This applies even if the "-" flag is also specified. So the last
>> example is meant to illustrate that 2 minuses don't make a plus here.
>
>
> That's very unusual, IMO. This behavior follows some SQL standard or is it
> an invention of PostgreSQL?
>

It's not part of the SQL standard, but it is based on C printf() and
friends from the Single UNIX Specification, see for example
http://pubs.opengroup.org/onlinepubs/7908799/xsh/fprintf.html

My reading of that is that "-" is to be treated as a flag, not as a
minus sign, so specifying it multiple times has the same effect as
specifying it once. On my linux box, the following both produce
left-justified output:

  printf("'%-10s'\n", "foo");
  printf("'%--10s'\n", "foo");

Regards,
Dean

(Please CC me the reply, since I'm not subscribed to the list.)

Dean Rasheed wrote:
> On 14 September 2013 09:29, rudolf <stu3.1@eq.cz> wrote:
>> The last example from
>> http://www.postgresql.org/docs/9.3/static/functions-string.html#FUNCTIONS-STRING-FORMAT
>> - "examples using width fields and the - flag" seems to be incorrect, see
>> the attached patch.
>
> No, the example is correct. Referring to the documentation above that:
>
>      If the width argument is negative, the result is left aligned (as
> if the - flag had been specified) ...
>
> This applies even if the "-" flag is also specified. So the last
> example is meant to illustrate that 2 minuses don't make a plus here.

That's very unusual, IMO. This behavior follows some SQL standard or is
it an invention of PostgreSQL?

Thanks,

r.

(Please CC me the reply, since I'm not subscribed to the list.)

Pavel Stehule wrote:
> 2013/9/17 rudolf
>     Dean Rasheed wrote:
[...]
>         This applies even if the "-" flag is also specified. So the last
>         example is meant to illustrate that 2 minuses don't make a plus
>         here.
>
>     That's very unusual, IMO. This behavior follows some SQL standard or
>     is it an invention of PostgreSQL?
>
> this is postgresql feature - standard doesn't support any similar
> functionality - and printf is some like developer Esperanto. We
> significantly reduced complexity of printf function and we modified
> basic rules for usage in SQL, but some very typical rules - like format
> placeholders, we share - we don't introduce own rules there.

Yes, as I already wrote to Dean (and forgot to cc the list), you are
right, the behavior is correct. Thanks for the explanation!

Kind regards,

r.