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
Show quoted text
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