Re: BUG #16804: substring() function returns "negative substring length" error when using a large length argument

po 4. 1. 2021 v 19:44 odesílatel PG Bug reporting form <
noreply(at)postgresql(dot)org> napsal:

> The following bug has been logged on the website:
>
> Bug reference: 16804
> Logged by: Rafi Shamim
> Email address: rafiss(at)gmail(dot)com
> PostgreSQL version: 13.1
> Operating system: MacOS 10.15.7
> Description:
>
> Reproduction steps:
>
> 1. Connect to any PostgreSQL database.
> 2. Run this query:
> > select substring('string' from 2 for 2147483646);
>
> Actual result:
>
> 2021-01-04 12:43:13.145 EST [85734] ERROR: negative substring length not
> allowed
> 2021-01-04 12:43:13.145 EST [85734] STATEMENT:s
> negative substring length not allowed
>
>
> Expected result:
>
> I don't know if this is covered by these docs:
> https://www.postgresql.org/docs/13/functions-string.html
> But I would expect one of the following:
> 1. There should be no error message, and the result should be 'tring'.
> (Meaning it just goes to the end of the string.)
> 2. An error message that says that the length argument is too long.
>

> I don't know what the SQL standard says, but when I try similar queries
> with
> SQLite and MSSQL, the result is 'tring'.
>

Minimally this is a bug and it should raise an error "integer out of
range". Probably in this case we can use MAX_INT as a special value of
unlimited length, although it is a little bit scary, because length is an
optional value. The attached patch should fix this issue. I do not have
access to Oracle to check the behaviour of this case there.

Regards

Pavel