Обсуждение: BUG #2739: INTERSECT ALL not working

The following bug has been logged online:

Bug reference:      2739
Logged by:          Mason Hale
Email address:      masonhale@gmail.com
PostgreSQL version: 8.1.5
Operating system:   GNU/Linux 2.6.9-42.0.3.ELsmp
Description:        INTERSECT ALL not working
Details:

'INTERSECT ALL' does not return duplicate rows in a query.

The query below should return 10 rows, but it returns 5 rows on my system:

(
   SELECT tablename
   FROM pg_tables
   LIMIT 5
)
INTERSECT ALL
(
   (
     SELECT tablename
     FROM pg_tables
     LIMIT 5
   )
   UNION ALL
   (
     SELECT tablename
     FROM pg_tables
     LIMIT 5
   )
)

Note, the above is a simplied query meant to demonstrate the problem. This
same behavior occurs (and was discovered) in real-world situations with
user-defined tables.

This is nearly a deal-stopper for our application. Please reply to let me
know the status of this report.

Thanks,
Mason Hale

"Mason Hale" <masonhale@gmail.com> writes:
> The query below should return 10 rows,

Not by my reading of the spec.  SQL92 7.10 saith:

            b) If a set operator is specified, then the result of applying
              the set operator is a table containing the following rows:

              i) Let R be a row that is a duplicate of some row in T1 or of
                 some row in T2 or both. Let m be the number of duplicates
                 of R in T1 and let n be the number of duplicates of R in
                 T2, where m >= 0 and n >= 0.

...

            iii) If ALL is specified, then

...


                 3) If INTERSECT is specified, then the number of duplicates
                   of R that T contains is the minimum of m and n.

You have m = 1, n = 2 for each distinct row at the INTERSECT step,
ergo you get one copy out.

            regards, tom lane

Tom -

Many thanks for the quick reply. I feel honored to receive email from you
after seeing your name so many times in my web searches on Postgres topics.

That's not how I understood INTERSECT ALL to work. But it's the clear the
spec is right and my understanding is wrong.
This is not a bug.

Unfortunately the INTERSECT ALL as spec'd and implemented doesn't quite give
me what I need. So back to the drawing board for me...

best regards,
Mason

On 11/6/06, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> "Mason Hale" <masonhale@gmail.com> writes:
> > The query below should return 10 rows,
>
> Not by my reading of the spec.  SQL92 7.10 saith:
>
>             b) If a set operator is specified, then the result of applying
>               the set operator is a table containing the following rows:
>
>               i) Let R be a row that is a duplicate of some row in T1 or
> of
>                  some row in T2 or both. Let m be the number of duplicates
>                  of R in T1 and let n be the number of duplicates of R in
>                  T2, where m >= 0 and n >= 0.
>
> ...
>
>             iii) If ALL is specified, then
>
> ...
>
>
>                  3) If INTERSECT is specified, then the number of
> duplicates
>                    of R that T contains is the minimum of m and n.
>
> You have m = 1, n = 2 for each distinct row at the INTERSECT step,
> ergo you get one copy out.
>
>                         regards, tom lane
>