Re: Undefined psql variables

On Mon, Jan 23, 2017 at 10:34 AM, Corey Huinker <corey(dot)huinker(at)gmail(dot)com>
wrote:

> I was giving some thought to how psql handles undefined variables.
>
> I would like an option where either psql can provide an alternate value
> when an undefined variable is referenced, or a way to detect that a
> specific variable is undefined and replace it with a defined variable.
>
> My first thought thought was to have a
>
>
> \set_if_undefined var_name 'default_value'
>
>
​\coalesce var_name [maybe other var names?] 'default_value' --sets the
value of var_name to itself or the first defined/non-null result of the
subsequent items​. Probably only useful if you allow expressions. I have
followed the "\if" thread that closely but IIRC that was part of the
discussion there.

>
> Another idea adding a \pset parameter that would return a specific value
> when an undefined psql variable is referenced instead of raising an error.
> Like this:
>
> # select :'x' as value_of_x;
> ERROR: syntax error at or near ":"
> LINE 1: select :'x' as value_of_x;
> ^
>
> # \pset variable_default ''
> analytics=# select :'x' as value_of_x;
> value_of_x
> ------------
>
> (1 row)
>
>
​-1​

I unconvinced that setting this in the global environment is a good thing.

David J.