Here’s a query that would give the wrong answer if you trim:
select count(*) from (
select deptno from scott.emp
union
select deptno from scott.dept);
returns 4. Note that ‘deptno’ is not used. But when I trim it away,
select count(*) from (
select 'a' from scott.emp
union
select 'a' from scott.dept);
returns 1. (I included ‘a’ because SQL doesn’t allow an empty SELECT clause. It
doesn’t affect the reasoning.)
Julian
> On Jun 2, 2021, at 6:03 AM, Sean Broeder <sbroe...@apache.org> wrote:
>
> Currently the RefFieldTrimmer only trims on a UNION ALL operation. I've
> been experimenting to see if it is also possible to trim on UNION
> DISTINCT. Is there a simple query that demonstrates why this is not
> possible?
>
> Thanks,
> Sean
