The following bug has been logged online:

Bug reference: 2739
Logged by: Mason Hale
Email address: masonhale (AT) gmail (DOT) 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

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"Mason Hale" <masonhale (AT) gmail (DOT) com> writes:
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

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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 (AT) sss (DOT) pgh.pa.us> wrote:
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Tom -<br><br>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.<br><br>That's not how I understood INTERSECT ALL to work. But it's the clear the spec is right and my understanding is wrong.
<br>This is not a bug.<br><br>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...<br><br>best regards,<br>Mason<br><br><div><span class="gmail_quote">
On 11/6/06, <b class="gmail_sendername">Tom Lane</b> &lt;<a href="mailto:tgl (AT) sss (DOT) pgh.pa.us">tgl (AT) sss (DOT) pgh.pa.us</a>&gt; wrote:</span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
&quot;Mason Hale&quot; &lt;<a href="mailto:masonhale (AT) gmail (DOT) com">masonhale (AT) gmail (DOT) com</a>&gt; writes:<br>&gt; The query below should return 10 rows,<br><br>Not by my reading of the spec.&nbsp;&nbsp;SQL92 7.10 saith:<br><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;b) If a set operator is specified, then the result of applying
<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbs p;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;the set operator is a table containing the following rows:<br><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;& nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;i) Let R be a row that is a duplicate of some row in T1 or of<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbs p; some row in T2 or both. Let m be the number of duplicates
<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbs p;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; of R in T1 and let n be the number of duplicates of R in<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbs p; T2, where m &gt;= 0 and n &gt;= 0.<br><br>...<br><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp ;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;iii) If ALL is specified, then<br><br>...<br><br><br>&nbsp;&nbsp;&nbsp;&nbsp ;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;& nbsp;&nbsp;&nbsp;&nbsp; 3) If INTERSECT is specified, then the number of duplicates
<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbs p;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp; of R that T contains is the minimum of m and n.<br><br>You have m = 1, n = 2 for each distinct row at the INTERSECT step,<br>ergo you get one copy out.<br><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbs p;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;regards, tom lane
<br></blockquote></div><br>

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