[Info-ingres] Ingres Star and group by.

[Karl Schendel]

> On Oct 20, 2021, at 7:21 AM, Adrian Williamson <adrian.williamson at rationalcommerce.com> wrote:
> ...
> In the star database:
>  
> register table  gt
> as link from grouptest1
> with node = 'nodey', database = 'number2';\g
>  
> select date_trunc('month',dt) , count(*) from gt group by 1;\g
>  
> +-------------------------+-------------+
> |col1                     |col2         |
> +-------------------------+-------------+
> |01-nov-2020              |            2|
> |01-nov-2020              |            2|
> |01-jul-2020              |            2|
> |01-jul-2020              |            2|
> |01-jan-2020              |            3|
> |01-jan-2020              |            3|
> |01-jan-2020              |            3|
> +-------------------------+-------------+
>  


You've (re)discovered issue II-5204 / 1083817.  Your SQL is correct.
Unfortunately, Star is assuming that user query constants always
point to the original constant text.  This isn't always true and one such
situation is the 'month' bit in the date_trunc function.  The full analysis
is complicated, but the end result is that opa thinks that there are two
different copies of date_trunc('month',dt) and generates a quel-like
linkback.  It's not immediately clear how to fix this; there are 3 or 4
possible ways forward, all involving a fair amount of work.

This was caused somewhere in the 10.x timeframe, it seems, as a side
effect of fixing a totally different bug where tree fragment comparisons
were too permissive and treated two different fragments as being the same.

Karl