Re: Empty VARCHAR parameters converted to NULL

I assume you're referring to input/output parameters where the input value
is NULL, but the output value is non-NULL?

The MSDN docs for rpcparam (
https://msdn.microsoft.com/en-us/library/aa937102(v=sql.80).aspx) don't
really indicate how this case is handled, but
I think the following would work for the input/output parameter:

maxlen = <maximum desired length of return value>
datalen = 0

Basically maxlen is used for the length of the output parameter buffer and
datalen is the length of the input data.

Thoughts?


On Tue, Mar 15, 2016 at 4:37 PM, Frediano Ziglio <[email protected]> wrote:

> I was looking at this issue. The problem raise when you want a return
> value but you want to pass a empty or a NULL varchar. How to
> differentiate in this case? value cannot be NULL for return
> parameters.
>
> Frediano
>
>
> 2016-01-19 18:25 GMT+00:00 Joshua Lang <[email protected]>:
> > I've read that older versions didn't even support passing 0-length data
> > (prior to TDS 7.0 I believe). If this could be supported for later
> versions
> > of TDS 7.0, that would be great.
> >
> > Thanks.
> >
> > On Tue, Jan 19, 2016 at 2:52 AM, Frediano Ziglio <[email protected]>
> wrote:
> >
> >> 2016-01-16 1:41 GMT+00:00 Joshua Lang <[email protected]>:
> >> > In the latest version of FreeTDS-dblib (0.95.79) I'm passing rpc
> VARCHAR
> >> > parameters of 0 length, but non-NULL (empty strings). FreeTDS seems to
> >> turn
> >> > these into NULL values before passing them on to SQL Server. From what
> >> I've
> >> > read, it seems as if older databases didn't support passing empty
> >> strings,
> >> > but newer ones do? (i.e. TDS 7.0+ do support empty strings).
> >> >
> >> > It seems as this is a known issue, but I was wondering if it is
> possible
> >> to
> >> > fix it for the newer versions of SQL server? E.g. in dbrpcparam()
> >> passing a
> >> > non-NULL pointer to the 'value' parameter and a 0 to 'datalen' would
> >> > indicate an empty string is desired if possible.
> >> >
> >> > Thoughts?
> >>
> >>
> >> The main problem is not libTDS (the code library) but dbrpcparam
> >> specification.
> >> datalen < 0 is invalid for variable fields (like VARCHAR) and 0 is used
> >> for NULL
> >> value (no matter the data pointer). But looks like your suggestion
> >> (not NULL value
> >> and 0 datalen) could be a good choice.
> >> Not sure however if this could work with all types and server versions
> >> (for instance
> >> 0 size TEXT).
> >> We can do it but I'm not thinking about backporting it to 0.95.
> >>
> >> Frediano
> >> _______________________________________________
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> >>
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