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From "Mike Matrigali (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-5702) Creating a foreign key constraint does not automatically create a statistics row if foreign key constraint will share a backing index created for a primary key
Date Fri, 20 Apr 2012 22:35:34 GMT

    [ https://issues.apache.org/jira/browse/DERBY-5702?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13258636#comment-13258636
] 

Mike Matrigali commented on DERBY-5702:
---------------------------------------

Is there any user level problem with this situation.  In this situation I think the optimizer
in the worst case sees 2 indexes that are on exactly the same keys in same order.  One index
is unique and one is not.  The optimizer should always choose the unique one, when it chooses
unique indexes it should never look at the statistics.  

If anyone chooses to fix this issue, they should look at optimizes creation of the statistic
row - at least for single column indexes.  There is no need to scan the whole table when you
know the underlying index is unique.  

I would rate this issue as minor, unless a user level issue is known.
                
> Creating a foreign key constraint does not automatically create a statistics row if foreign
key constraint will share a backing index created for a primary key
> ---------------------------------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: DERBY-5702
>                 URL: https://issues.apache.org/jira/browse/DERBY-5702
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 10.8.2.2
>            Reporter: Mamta A. Satoor
>
> When a foreign key constraints is created on a column which already has a primary key
constraint, the statistics for foreign key constraint do not get created automatically. Have
to run update statistics by hand to add statistics for foreign key constraint. I hope my understanding
of statistics creation is correct in this regards. Following script shows the issue
> java -Dderby.storage.indexStats.auto=false -Dij.exceptionTrace=true org.apache.derby.tools.ij
> connect 'jdbc:derby:db1;create=true'; 
> CREATE TABLE TEST_TAB_1 
> ( 
>     ID INTEGER NOT NULL primary key
> ); 
> CREATE TABLE TEST_TAB_2 
> ( 
>    ID INTEGER not null, ID1 INTEGER not null
> ); 
> insert into TEST_TAB_1 values (1); 
> insert into test_tab_2 values(1,1);
> CALL SYSCS_UTIL.SYSCS_UPDATE_STATISTICS('APP','TEST_TAB_1', null); 
> CALL SYSCS_UTIL.SYSCS_UPDATE_STATISTICS('APP','TEST_TAB_2', null); 
> --At this point, we will find statistics row for primary key constraint on TEST_TAB_1
> select 
> c.TABLEID, 
> c.CONGLOMERATENUMBER, 
> c.CONGLOMERATENAME, 
> c.ISINDEX, 
> c.ISCONSTRAINT, 
> c.CONGLOMERATEID, 
> t.TABLEID, 
> t.TABLENAME, 
> t.TABLETYPE, 
> s.STATID, 
> s.REFERENCEID, 
> s.TABLEID, 
> s.CREATIONTIMESTAMP, 
> s.TYPE, 
> s.VALID, 
> s.COLCOUNT, 
> CAST(STATISTICS AS VARCHAR(40)) as STATISTICS 
> from sys.SYSCONGLOMERATES c join sys.SYSTABLES t on c.TABLEID = t.TABLEID join sys.SYSSTATISTICS
s on s.TABLEID = t.TABLEID 
> where t.TABLENAME = 'TEST_TAB_1' and c.ISINDEX = false; 
> --Now create primary key constraint on TEST_TAB_2 
> ALTER TABLE TEST_TAB_2 
>                 ADD CONSTRAINT TEST_TAB_2_PK_1
>         		PRIMARY KEY (id);
> --At this point, we will find statistics row for primary key constraint on TEST_TAB_2
> select 
> c.TABLEID, 
> c.CONGLOMERATENUMBER, 
> c.CONGLOMERATENAME, 
> c.ISINDEX, 
> c.ISCONSTRAINT, 
> c.CONGLOMERATEID, 
> t.TABLEID, 
> t.TABLENAME, 
> t.TABLETYPE, 
> s.STATID, 
> s.REFERENCEID, 
> s.TABLEID, 
> s.CREATIONTIMESTAMP, 
> s.TYPE, 
> s.VALID, 
> s.COLCOUNT, 
> CAST(STATISTICS AS VARCHAR(40)) as STATISTICS 
> from sys.SYSCONGLOMERATES c join sys.SYSTABLES t on c.TABLEID = t.TABLEID join sys.SYSSTATISTICS
s on s.TABLEID = t.TABLEID 
> where t.TABLENAME = 'TEST_TAB_2' and c.ISINDEX = false; 
> --Now if we create a foreign key constraint on TEST_TAB_2(ID), there will be no statistics
created for it.
> ALTER TABLE TEST_TAB_2
>                 ADD CONSTRAINT TEST_TAB_2_FK_1 
>         		FOREIGN KEY(id) REFERENCES TEST_TAB_1(id);
> --still only one statistics row for TEST_TAB_2
> select 
> c.TABLEID, 
> c.CONGLOMERATENUMBER, 
> c.CONGLOMERATENAME, 
> c.ISINDEX, 
> c.ISCONSTRAINT, 
> c.CONGLOMERATEID, 
> t.TABLEID, 
> t.TABLENAME, 
> t.TABLETYPE, 
> s.STATID, 
> s.REFERENCEID, 
> s.TABLEID, 
> s.CREATIONTIMESTAMP, 
> s.TYPE, 
> s.VALID, 
> s.COLCOUNT, 
> CAST(STATISTICS AS VARCHAR(40)) as STATISTICS 
> from sys.SYSCONGLOMERATES c join sys.SYSTABLES t on c.TABLEID = t.TABLEID join sys.SYSSTATISTICS
s on s.TABLEID = t.TABLEID 
> where t.TABLENAME = 'TEST_TAB_2' and c.ISINDEX = false; 
> --Running statistics creation by hand will create 2nd statistics row for TEST_TAB_2
> CALL SYSCS_UTIL.SYSCS_UPDATE_STATISTICS('APP','TEST_TAB_2', null); 
> -- now will have 2 statistics rows for TEST_TAB_2
> select 
> c.TABLEID, 
> c.CONGLOMERATENUMBER, 
> c.CONGLOMERATENAME, 
> c.ISINDEX, 
> c.ISCONSTRAINT, 
> c.CONGLOMERATEID, 
> t.TABLEID, 
> t.TABLENAME, 
> t.TABLETYPE, 
> s.STATID, 
> s.REFERENCEID, 
> s.TABLEID, 
> s.CREATIONTIMESTAMP, 
> s.TYPE, 
> s.VALID, 
> s.COLCOUNT, 
> CAST(STATISTICS AS VARCHAR(40)) as STATISTICS 
> from sys.SYSCONGLOMERATES c join sys.SYSTABLES t on c.TABLEID = t.TABLEID join sys.SYSSTATISTICS
s on s.TABLEID = t.TABLEID 
> where t.TABLENAME = 'TEST_TAB_2' and c.ISINDEX = false; 
> --If I create foreign key on a column that does not share backing index with primary
key, stats will get created automatically
> ALTER TABLE TEST_TAB_2
>                 ADD CONSTRAINT TEST_TAB_2_FK_2 
>         		FOREIGN KEY(id1) REFERENCES TEST_TAB_1(id);
> --will have additional constraint row for new foreign key constraint on TEST_TAB_2
> select 
> c.TABLEID, 
> c.CONGLOMERATENUMBER, 
> c.CONGLOMERATENAME, 
> c.ISINDEX, 
> c.ISCONSTRAINT, 
> c.CONGLOMERATEID, 
> t.TABLEID, 
> t.TABLENAME, 
> t.TABLETYPE, 
> s.STATID, 
> s.REFERENCEID, 
> s.TABLEID, 
> s.CREATIONTIMESTAMP, 
> s.TYPE, 
> s.VALID, 
> s.COLCOUNT, 
> CAST(STATISTICS AS VARCHAR(40)) as STATISTICS 
> from sys.SYSCONGLOMERATES c join sys.SYSTABLES t on c.TABLEID = t.TABLEID join sys.SYSSTATISTICS
s on s.TABLEID = t.TABLEID 
> where t.TABLENAME = 'TEST_TAB_2' and c.ISINDEX = false; 

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