Re: proposal - assign result of query to psql variable - Mailing list pgsql-hackers

2012/10/15 Pavel Stehule <pavel.stehule@gmail.com>:
> 2012/10/15 Shigeru HANADA <shigeru.hanada@gmail.com>:
>> Hi Pavel,
>>
>> First of all, I'm sorry that my previous review was rough.  I looked
>> your patch and existing code closely again.
>>
>> On 2012/10/15, at 12:57, Pavel Stehule <pavel.stehule@gmail.com> wrote:
>>> 2012/10/14 Tom Lane <tgl@sss.pgh.pa.us>:
>>>> * ExecQueryUsingCursor's concept of how to process command results
>>>>  (why? surely we don't need \gset to use a cursor)
>>>
>>> There was two possibilities, but hardly non using cursor is better way
>>
>> +1 for supporting the case when FETCH_COUNT > 0, because user might set
>> so mainly for other queries, and they would want to avoid changing
>> FETCH_COUNT setting during every query followed by \gset.
>>
>>>> * the psql lexer (adding a whole bunch of stuff that probably doesn't
>>>>  belong there)
>>>
>>> ??
>>
>> I think that Tom is talking about psql_scan_slash_vars().  It seems too
>> specific to \gset command.  How about to improve
>> psql_scan_slash_options() so that it can handle comma-separated variable
>> list?  Although you might have tried it before.
>> # Unused OT_VARLIST macro gave me the idea.
>
> yes, it is possible - I'll look on it at evening

a reuse of psql_scan_slash_options is not good idea - a interface of
this function is out of my purposes - and I cannot to signalise error
from this procedure. But I can minimize psql_scan_slash_var and I can
move lot of code out of lexer file.

>
>>
>>>> * the core psql settings construct (to store something that is in
>>>>  no way a persistent setting)
>>>>
>>>
>>> ??
>>
>> I thought that having \gset arguments in pset is reasonable, since \g
>> uses pest.gfname to hold its one-shot setting.  Or, we should refactor
>> \g to fit with \gset?  I might be missing Tom's point...
>>
>>>> Surely there is a less ugly and invasive way to do this.  The fact
>>>> that the reviewer keeps finding bizarre bugs like "another backslash
>>>> command on the same line doesn't work" seems to me to be a good
>>>> indication that this is touching things it shouldn't.
>>>
>>> - all these bugs are based on lexer construct. A little modification
>>> of lexer is possible
>>
>> IMHO those issues come from the design rather than the implementation of
>> lexer.  AFAIK we don't have consensus about the case that both of \g and
>> \gset are used for a query like this:
>>
>> postgres=# SELECT 1 \gset var \\ \g foo.txt
>>
>> This seems regal.  Should we store "1" into var and write the result
>> into foo.txt?  Or, only either of them?  It's just an idea and it
>> requires new special character, but how about use \g command for file,
>> pipe, and variable?  In the case we choose '&' for variable prefix:
>>
>> postgres=# SELECT 'hello', 'wonderful', 'world!' \g &var1,,var2
>>
>> Anyway, we've had no psql's meta command which processes query result
>> other than \g.  So, we might have more considerable issues about design.
>
> a current design is rigid - a small implementation can stop parsing
> target list, when other backslash statement is detected
>
>>
>> BTW, what the word "comma_expected" means?  It's in the comment above
>> psql_scan_slash_vars().  It might be a remaining of old implementation.
>
> This identifier is mistaken - etc this comment is wrong and related to
> old implementation - sorry. A first design was replaced by state
> machine described by  VarListParserState
>
>
>
>>
>> Regards,
>> --
>> Shigeru HANADA
>> shigeru.hanada@gmail.com
>>
>>
>>
>>
>>