[
https://issues.apache.org/jira/browse/DERBY-3603?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12587894#action_12587894
]
Thomas Nielsen commented on DERBY-3603:
---------------------------------------
Looking at the queryplans I see something quite interesting.
Both queries S2 and S3 end up with the same query plan. The top looking like
this:
Scalar
|
PRN
|
NestedLoop ExistsJoin
/ \
NestedLoopExistsJoin IndexScanResultSet
/ \ |
... ... ...
The interesting stuff happens in the lower, right-hand IndexScanResultSet
(let's call it ISR1)
In the correct 3-row query S3, ISR1 sees 3 rows and qualifies 3 rows.
In the incorrect 2-row query S2, ISR1 seens 3 rows, but only qualifies 2 of
them.
So for S2, this becomes
Scalar
("2")
|
PRN
(2 rows)
|
NestedLoop ExistsJoin
(3 rows L, 2 rows R)
/ \
NestedLoopExistsJoin IndexScanResultSet
(3 rows L, 3 rows R) (sees 3 rows, qualifies 2 rows)
/ \ |
... ... ...
The query plan for both S2 and S3 state that ISR1 is an
"Index Scan ResultSet for ADMIN_UNITS using constraint ADMIN_UNIT_ID_PK at read
committed isolation level using share row locking chosen by the optimizer".
Next task would be to find out why ISR1 rejects/discards the third row in S2,
and not in S3.
> 'IN' clause ignores valid results, incorrect qualifier handling suspected
> -------------------------------------------------------------------------
>
> Key: DERBY-3603
> URL: https://issues.apache.org/jira/browse/DERBY-3603
> Project: Derby
> Issue Type: Bug
> Components: SQL
> Affects Versions: 10.3.2.1, 10.4.1.1
> Reporter: David Butterworth
> Attachments: derbydb.jar, derbydb.tar.bz2
>
>
> Derbys' 'IN' clause is returning different results depending on which side of
> a joined table
> I am doing my 'IN' comparison against. This only occurs when the number of
> items within the 'IN' clause is greater then 1.
> This behaviour was also confirmed by Bryan Pendleton in this thread:
> http://mail-archives.apache.org/mod_mbox/db-derby-user/200804.mbox/[EMAIL
> PROTECTED]
> Using the test database attatched the following 2 queries produce the issue:
> ij> select count(*) FROM spike.accounts account, spike.admin_units
> admin_unit,
> spike.bookings booking
> WHERE booking.child_id = 2 AND
> admin_unit.admin_unit_id IN (1,21) AND
> booking.booking_date_time_out >= 20080331000000 AND
> booking.booking_date_time_in <= 20080406235900 AND
> account.account_id = booking.account_id AND
> admin_unit.admin_unit_id = account.admin_unit_id;
> 1
> -----------
> 2
> 1 row selected
> ij> select count(*) FROM spike.accounts account, spike.admin_units admin_unit,
> spike.bookings booking
> WHERE booking.child_id = 2 AND
> account.admin_unit_id IN (1,21) AND
> booking.booking_date_time_out >= 20080331000000 AND
> booking.booking_date_time_in <= 20080406235900 AND
> account.account_id = booking.account_id AND
> admin_unit.admin_unit_id = account.admin_unit_id;
> 1
> -----------
> 3
> 1 row selected
> ij>
> The only difference between the 2 statements is which side of a join the 'IN'
> clause is matched against.
> Bryan performed some initial testing and stated the following:
> --------------------- SNIP ------------------------
> Interestingly, although the actual results do NOT contain any values
> for admin_unit_id = 21, if I change the query to:
> admin_unit.admin_unit_id IN (1)
> or
> account.admin_unit_id IN (1)
> then the problem disappears -- I get 3 rows for both queries.
> I also ran query plans for both the queries (in the IN (1,21) case)
> and have pasted the (simplified) query plans at the end of this message.
> I notice that in the case where the query gives 2 rows, which is
> when we specify admin_unit.admin_unit_id in (1,21), the admin_unit_id
> index scan output in the query plan contains:
> qualifiers:
> Column[0][0] Id: 0
> Operator: =
> Ordered nulls: false
> Unknown return value: false
> Negate comparison result: false
> However, in the case where the query gives 3 rows, which is
> when we specify account.admin_unit_id in (1,21), the admin_unit_id
> index scan output in the query plan contains:
> qualifiers:
> None
> I think it is the presence/absence of this qualifier on the query
> scan which is causing the different results in the query, as in
> the first case we see:
> Number of rows qualified=2
> Number of rows visited=3
> but in the second case we see:
> Number of rows qualified=3
> Number of rows visited=3
> I definitely don't have any explanation for why you are getting
> this odd behavior; it certainly seems like a bug to me.
> -------------END SNIP -----------------------
--
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.
