Oracle 11g BUG when using deferred constraints

Found a BUG when using deferred constraints on Oracle DB version Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production.

Here is the test case:
First we create two tables. Table P1 is the parent table, which has a primary key on column ID. The second table C1 is a table (child) with a foreign key constraint which is deferrable and references the parent table.

Create the two tables:

CREATE TABLE P1 (ID NUMBER);
CREATE TABLE C1 (ID NUMBER, X VARCHAR2(2));

Create the primary key and foreign key constraints:

ALTER TABLE P1 ADD CONSTRAINT PK_ID PRIMARY KEY (ID);
ALTER TABLE C1 ADD CONSTRAINT FK_P1_ID FOREIGN KEY (ID) REFERENCES P1 (ID) DEFERRABLE;

We insert same test data into the two tables:

INSERT INTO P1 VALUES (1);
INSERT INTO C1 VALUES (1,'X1');
INSERT INTO C1 VALUES (1,'X2');

Now we create the test to delete some data, while switching the constraints to deferred. We try to delete the "parent" record, and one delete one of the child records in the child table. We leave on child record. After the delete statements we switch back the constraints to immediate:

SET CONSTRAINTS ALL DEFERRED;

DELETE P1 WHERE ID = 1;
DELETE C1 WHERE X = 'X1';

SET CONSTRAINTS ALL IMMEDIATE;

When we execute the final statement (SET CONSTRAINTS ALL IMMEDIATE) we get an error ORA-02292: integrity constraint (schema.FK_P1_ID) violated - child record found.

This is what we expected and is of course correct.

But here is the trick. If we add an index to the table C1 on column ID something weird happens.
Lets create an index:

CREATE INDEX IND_1 ON C1 (ID);

Now we try the test again:

SET CONSTRAINTS ALL DEFERRED;

DELETE P1 WHERE ID = 1;
DELETE C1 WHERE X = 'X1';

SET CONSTRAINTS ALL IMMEDIATE;

After executing the last statement we would expect the same error as we got before, but we didn't receive any error. We corrupted the data and now have corrupt data in the database. If we now look at the data in the two tables, we can see that the parent record is deleted, and we also deleted one child record, but the second child record is in the database and the table has a foreign key which references to the parent table:

SELECT * FROM P1;
SELECT * FROM C1;

Cloud computing?

First non technical post from me. Cloud computing isn't a new idea, but I found video (audio), which I totaly agree with about cloud computing. Thought I was the only one who thinks like this, apparently not :)

Creating materialized views

Materialized views are a great way of keeping the same data at two different locations (databases).

At the "source" database you have to create a materialized view log on the desired table. You do this with the following command:

create materialized view log on TEST_TABLE with sequence, primary key including new values;

The above command is used when the table has primary key.

When you execute the above command two system tables are generated:
- mlog$_test_table - log table for the changes made to the source table
- rupd$_test_table - log table for controlling the correct order of changes, when a table has primary key

The "destination" database has to have select privileges on the source table (test_table) and the log table (mlog$_test_table).
At the "destination" database execute the following command:

create materialized view TEST_TABLE refresh fast on demand enable query rewrite as select * from TEST_TABLE@SOURCE_DB_LINK ;

You have different options to control writing the changes to the destination, either the refresh fast or refress complete. More on this can be found here.

To manualy copy the changes from the source to the destination database, execute the following command on the destination database:

begin
dbms_mview.refresh('TEST_TABLE');
end;

UTL_MATCH

Came across an interesting Oracle supplied package called UTL_MATCH. It is used for comparing string values. If for example you want the user to be 90% exact when typing a certain string value you can use the function edit_distance_similarity and embed it into a program logic.

select UTL_MATCH.edit_distance_similarity ('programmer', 'programer')
from dual;

Detailed description of the package can be found here

Generating documentation from the database

Made a relatively simple function that generates HTML output of all the database objects which can be used as a database documentation if used correctly.

The whole function can be downloaded here.

Working with Oracle object types based on XSD schemas

Attended the SIOUG (Slovenian Oracle User Group) Conference 2010, where I had a lecture "Working with Oracle object types based on XSD schemas".

The power point presentation can be downloaded here (some text is in slovenian language!):
- PPTX format
- PPT format

Reading XML data directly from web

The following select statement reads the data directly from the specified URL and displayes the result as an SQL result:

select to_date(a.extract('tecajnica/@datum','xmlns="http://www.bsi.si"').getstringval(), 'YYYY-MM-DD') as datum
, b.extract('tecaj/@oznaka','xmlns="http://www.bsi.si"').getstringval() as oznaka
, b.extract('tecaj/@sifra','xmlns="http://www.bsi.si"').getstringval() as sifra
, to_number(b.extract('tecaj/text()','xmlns="http://www.bsi.si"').getstringval(),'999999999999999D9999999999', 'NLS_NUMERIC_CHARACTERS=''.,''') as tecaj
from table(xmlsequence(xmltype(urifactory.getUri('http://www.bsi.si/_data/tecajnice/dtecbs-l.xml').getclob()
).extract('DtecBS/tecajnica','xmlns="http://www.bsi.si"')
)
) a
, table(xmlsequence(a.extract('tecajnica/tecaj','xmlns="http://www.bsi.si"'))) b
;