Re: proposal - assign result of query to psql variable

2013/2/2 Tom Lane <tgl@sss.pgh.pa.us>:
> Shigeru Hanada <shigeru.hanada@gmail.com> writes:
>> On Sat, Feb 2, 2013 at 7:30 PM, Pavel Stehule <pavel.stehule@gmail.com> wrote:
>>> possible variants
>>>
>>> a) don't store NULL  values - and remove existing variable when NULL
>>> be assigned - it is probably best, but should be confusing for users
>>> b) implement flag IS NULL - for variables
>>> c) use nullPrint
>>> d) use empty String
>
>> +1 for a).  If users want to determine whether the result was NULL, or
>> want to use substitute string for NULL result, they can use coalesce
>> in SELECT clause.  Anyway the feature should be documented clearly.
>
> Yeah, I was considering that one too.  Let's do it that way.
>
>                         regards, tom lane

possible simple enhancing of this behave (for 9.4).

now missing variables is replaced by variable's name. We can implement
some pset option - some like define what do with missing variable

\pset missing_variable (use_name | use_null | error )

when this option will be active, then missing variable will be
replaced by NULL. With this feature sequences of SQL statements joined
by some variables can work.

SELECT NULL as myvar \gset
\pset missing_variable use_null
SELECT :'myvar' IS NULL;

ideas, opinions ?

Regards

Pavel