|
Problem IC73581
|
Status: Closed |
NESTED-LOOP JOIN WITH EARLYOUT FOR GROUPBY CLAUSES, YIELDS INCORRECT RESULTS WHEN JOIN COLUMNS ARE OF DIFFERENT DATA TYPES |
| product: |
DB2 FOR LUW / DB2FORLUW / 970 - DB2 |
| Problem description: |
When a query that meets all the following conditions is
executed, fewer results may be returned:
- Several tables are joined using columns with different data
types
- Nested-loop join is selected as the join method
- The output from the nested-loop join method is included into
the Group by clause and the Early Out flag is marked as GROUPBY
The following scenarios indicate the problem:
1. Joining two tables with different data types. To demonstrate
this problem, create two tables for the test. Create the tables
such that the columns being joined (t1.i1 and t2.i1) have
different data types.
create table t1 (i1 bigint not null, c2 char(250))
create index i1 on t1 (i1)
create table t2 (i1 smallint not null, i2 bigint)
create index i2 on t2 (i1,i2)
2. Run the query with different data types (bigint and smallint)
in predicate and the result goes directly into the Group by
clause.
select t2.i1, max(t2.i2) from t1, t2 where t1.i1=t2.i1 group by
t2.i1
3. When the Nested-loop join is selected as the join method.
Access Plan:
-----------
Total Cost: 22.8806
Query Degree: 1
Rows
RETURN
( 1)
Cost
I/O
|
99
GRPBY
( 2)
22.8709
3
|
99
^NLJOIN
( 3)
22.8655
3
/-----+------\
99 12.1111
IXSCAN IXSCAN
( 4) ( 5)
0.0455361 7.57676
0 1
| |
99 1199
INDEX: DB2INST1 INDEX: DB2INST1
I1 I2
Q2 Q1
3) NLJOIN: (Nested Loop Join)
Arguments:
---------
EARLYOUT: (Early Out flag)
GROUPBY
Predicates:
----------
3) Predicate used in Join
Predicate Text:
--------------
(Q2."I1" = Q1."I1") |
| Problem Summary: |
****************************************************************
* USERS AFFECTED: *
* All users. *
****************************************************************
* PROBLEM DESCRIPTION: *
* When a query that meets all the following conditions is *
* executed, fewer results may be returned: *
* - Several tables are joined using columns with different *
* data types *
* - Nested-loop join is selected as the join method *
* - The output from the nested-loop join method is included *
* into the Group by clause and the Early Out flag is marked as *
* GROUPBY *
* *
* The following scenarios indicate the problem: *
* *
* 1. Joining two tables with different data types. To *
* demonstrate this problem, create two tables for the test. *
* Create the tables such that the columns being joined (t1.i1 *
* and t2.i1) have different data types. *
* create table t1 (i1 bigint not null, c2 char(250)) *
* create index i1 on t1 (i1) *
* create table t2 (i1 smallint not null, i2 bigint) *
* create index i2 on t2 (i1,i2) *
* 2. Run the query with different data types (bigint and *
* smallint) in predicate and the result goes directly into the *
* Group by clause. *
* select t2.i1, max(t2.i2) from t1, t2 where t1.i1=t2.i1 group *
* by t2.i1 *
* 3. When the Nested-loop join is selected as the join method. *
* *
* Access Plan: *
* ----------- *
* Total Cost: 22.8806 *
* Query Degree: 1 *
* Rows *
* RETURN *
* ( 1) *
* Cost *
* I/O *
* | *
* 99 *
* GRPBY *
* ( 2) *
* 22.8709 *
* 3 *
* | *
* 99 *
* ^NLJOIN *
* ( 3) *
* 22.8655 *
* 3 *
* /-----+------\ *
* 99 12.1111 *
* IXSCAN IXSCAN *
* ( 4) ( 5) *
* 0.0455361 7.57676 *
* 0 1 *
* | | *
* 99 1199 *
* INDEX: DB2INST1 INDEX: DB2INST1 *
* I1 I2 *
* Q2 Q1 *
* 3) NLJOIN: (Nested Loop Join) *
* Arguments: *
* --------- *
* EARLYOUT: (Early Out flag) *
* GROUPBY *
* Predicates: *
* ---------- *
* 3) Predicate used in Join *
* Predicate Text: *
* -------------- *
* (Q2."I1" = Q1."I1") *
****************************************************************
* RECOMMENDATION: *
* Upgrade to DB2 9.7.0.4. *
**************************************************************** |
| Local Fix: |
Execute the following and then recycle the instance:
db2set DB2_REDUCED_OPTIMIZATION=NO_NLJN_EO_FOR_GB |
| available fix packs: |
DB2 Version 9.7 Fix Pack 4 for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 5 for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 6 for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 7 for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 8 for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 9 for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 9a for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 10 for Linux, UNIX, and Windows
|
| Solution |
The problem was fixed in DB2 9.7.0.4. |
| Workaround |
not known / see Local fix |
| Timestamps |
Date - problem reported :
Date - problem closed :
Date - last modified :
| 29.12.2010
20.04.2011
20.04.2011 |
| Problem solved at the following versions (IBM BugInfos) |
9.7.0.4
|
| Problem solved according to the fixlist(s) of the following version(s) |
| 9.7.0.4
|
 |
