On 4-10-2011 17:27, Paul Vinkenoog wrote:
> Dmitry wrote:
>
>>> 'YESTERDAY', 'TODAY' and 'TOMORROW'
>>> These are not context variables, but serve the same purpose. See 'NOW',
>>> which is also documented under Context variables (quotes and all).
>>
>> They can behave as either literals substituted immediately (timestamp
>> 'today') or as context variables (cast('today' as timestamp)). Quite
>> weird and perhaps even annoying, I know.
>
> Yes, we'll have to document this clearly:
>
> - When used with CAST() they are evaluated each time the code is executed and
> return the current date (or, in the case of 'now', timestamp). In this case,
> they are more up-to-date than the CURRENT_<DATETIME> variables, which are
> evaluated once per request (thus staying the same during a PSQL module
> execution, for instance).
>
> - When used as shorthand casts / datetime literals they are evaluated only
> once: at parse/prepare time. In this case, they are often *less* up-to-date
> than the CURRENT_<DATETIME> variables, because the latter are refreshed
> every time a prepared query is executed again.
To me this difference sounds like a bug, not a 'feature'.
--
Mark Rotteveel
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