Re: [Firebird-devel] Evaluation of derived tables and CTE's

[Dmitry Y. <fir...@ya...>]

12.07.2012 19:44, Paul Vinkenoog wrote:
>
> So... have we implemented the DT and CTE features correctly?

I believe it has nothing to do with our implementation of DTs and CTEs. 
Create a view with gen_id and and select that field thrice - you will 
get the same result. And views are here for a few decades ;-)

The "problem" is kinda conceptual. In regular selects and joins, only 
persistent fields compose an in-memory tuple, expressions are a separate 
thing and they are always evaluated per reference. If you reference them 
thrice, you will have three subsequent executions.


Dmitry