Re: proposal: condition blocks in psql

>>> \if_ver_eq 9.2
>>
>>  What do you thinking about it?
>>
>> Couldn't this kind of thing be done directly with PL/pgSQL?
>
> you can use PL/pgSQL - but there are some limits
>
> * maintenance large plpgsql functions

I agree with large but that would not necessarily mean complex. Also, some 
functions could be in SQL, and just the logic with PL/pgSQL.

> * the plpgsql functions or anonymous functions create a transaction borders
> - what should not be wanted

Hmmm... If something fails when installing an extension, a transaction 
border is probably a good thing? Also, the interaction of \if with 
possible BEGIN/COMMIT can lead to strange states.

> * I cannot to use psql variables simply in plpgsql code (plpgsql has not
> any macro language)

You can call a function with a variable as an argument:
  \set foo 1234  SELECT some_function(:foo);

> - so some patterns are implemented in plpgsql less readable

Which pattern?

> for example, if you can create a script that create some plpgsql function
> for specified PostgreSQL version, then using PLpgSQL for this purpose is
> suboptimal due less readability and maintainability

I'm not that sure about the qualitative assessment, "DO" looks pretty neat 
to me.

Moreover this is to be balanced with creating a scope/block/nesting system 
in psql which is currently alien to it and would bring its own pitfalls: 
psql is really intrinsically line/statement oriented, that would not be 
the case with what you're proposing as this logic would be deeply changed, 
and people would get stuck within a non-closed \if, this would interact 
with \i in possibly strange ways, and so on (say you include a file with a 
non closed \if, and then everything you type seems to be ignored, or 
a BEGIN is done in an if but the COMMIT was in another which was not 
activated because the conditions where not consistent...).

Basically, it looks like a potential Pandora box which is best left with 
its lid on.

-- 
Fabien.