Re: proposal: session server side variables

2017-01-01 11:28 GMT+01:00 Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>:

>
> Hello Pavel, and Happy new year!
>
> (1) Having some kind of variable, especially in interactive mode, allows to
>>>
>>>> manipulate previous results and reuse them later, without having to
>>>>> resort to repeated sub-queries or to retype non trivial values.
>>>>>
>>>>> Client side psql :-variables are untyped and unescaped, thus not very
>>>>> convenient for this purpose.
>>>>>
>>>>
>>>> You can currently (ab)use user defined GUCs for this.
>>>>
>>>
>>> How? It seems that I have missed the syntax to assign the result of a
>>> query to a user-defined guc, and to reuse it simply in a query.
>>>
>>
> postgres=# select set_config('myvar.text', (select
>> current_timestamp::text), false);
>>
>
> Thanks for the pointer! The documentation is rather scarse...
>
> They are indeed session or transaction-alive. They seem to be
> user-private, which is good. However they are text only, casts are needed
> in practice as shown by your example, and I find the syntax quite
> unfriendly for interactive use. I'm not sure about performance.
>

With some simple getter/setter functions you can get better comfort.

For not text variables you needs one cast more - probably only "date"
"timestamp" can be noticeable slower.

Regards

Pavel

>
> I have added a subsection about them in the wiki.
>
> --
> Fabien.
>