Re: pgbench - add \if support

Helo Craig,

> I'm a smidge worried about this. It seems like psql is growing a 
> scripting language.

The patch is about aligning pgbench with psql, which already has \if.

> Do we want to go our own way with a kind of organically grown
> scripting system? Or should we be looking at embedding client-side
> scripting in a more structured, formal way instead? Embed a lua interpreter
> or something?

My 0.02€ is that the point is to deal with useful/needed simple client 
capabilities while integrating gracefully with bare server-side executed 
SQL.

As for useful client-side capabilities, for both psql & pgbench ISTM that 
it is more in line with a limited cpp-like thing: include, expressions, 
variables, conditions... maybe minimal error handling. No loop.

As for a language interpreter, it would raise the question of which 
language (lua, tcl, python, perl, VB, sh, R, ...) and the graceful (upward 
compatible) integration of any such language: eg how do have pieces of 
bare SQL and any other existing language would require some scanning 
conventions that do not exist.

psql & pgbench already have ":x" variables. psql has the ability to set 
variable from SQL (\gset), and pgbench could do limited expressions to set 
these variables with (\set), which have been extended to be more complete 
, and there was use cases which motivate an (\if).

ISTM enough to align both tools for reasonnably simple use cases that 
could arise when running a basic SQL script of bench. If you have 
something really complicated, then full fledge programming is the answer, 
which cannot be bare-SQL compatible.

So the answer is that it is okay to aim at "limited" scripting because it 
covers useful use cases.

-- 
Fabien.