Insert problem using a SELECT from table with a index by function TRUNC

Question

I came across this problem when trying to insert from a select statement, the select returns the correct results however when trying to insert the results into a table, the results differ. I have found a work around by forcing an order by on the select, but surely this is an Oracle bug as how can the select statements value differ from the insert?
Platform: Windows Server 2008 R2
Oracle 11.2.3 Enterprise edition
(I have not tried to replicate this on other versions)
Here are the scripts to create the two tables and source data:
CREATE TABLE source_data
  ID                 NUMBER(2),
  COUNT_DATE       DATE
CREATE INDEX IN_SOURCE_DATA ON SOURCE_DATA (TRUNC(count_date, 'MM'));
INSERT INTO source_data VALUES (1, TO_DATE('20120101', 'YYYYMMDD'));
INSERT INTO source_data VALUES (1, TO_DATE('20120102', 'YYYYMMDD'));
INSERT INTO source_data VALUES (1, TO_DATE('20120103', 'YYYYMMDD'));
INSERT INTO source_data VALUES (1, TO_DATE('20120201', 'YYYYMMDD'));
INSERT INTO source_data VALUES (1, TO_DATE('20120202', 'YYYYMMDD'));
INSERT INTO source_data VALUES (1, TO_DATE('20120203', 'YYYYMMDD'));
INSERT INTO source_data VALUES (1, TO_DATE('20120301', 'YYYYMMDD'));
INSERT INTO source_data VALUES (1, TO_DATE('20120302', 'YYYYMMDD'));
INSERT INTO source_data VALUES (1, TO_DATE('20120303', 'YYYYMMDD'));
CREATE TABLE result_data
  ID                 NUMBER(2),
  COUNT_DATE       DATE
);Now run the select statement:
SELECT id, TRUNC(count_date, 'MM')
FROM source_data
GROUP BY id, TRUNC(count_date, 'MM')You should get the following:
1     2012/02/01
1     2012/03/01
1     2012/01/01Now insert into the results table:
INSERT INTO result_data
SELECT id, TRUNC(count_date, 'MM')
FROM source_data
GROUP BY id, TRUNC(count_date, 'MM');Select from that table and you get:
1     2012/03/01
1     2012/03/01
1     2012/03/01The most recent month is repeated for each row.
Truncate your table and insert with the following statement and the results should now be correct:
INSERT INTO result_data
SELECT id, TRUNC(count_date, 'MM')
FROM source_data
GROUP BY id, TRUNC(count_date, 'MM')
ORDER BY 1, 2;If anyone has encountered this behavior before could you please let me know, I can't see that I am making a mistake as the selects results are correct they should not differ from what is being inserted.
Edited by: user11285442 on May 13, 2013 5:16 AM
Edited by: user11285442 on May 13, 2013 6:15 AM

Answer 1

Hi,
welcome to the forum. I cannot reproduce the same behavior.
Could you please post the SQLPlus output while executing all commands, like it has been done by S10390?
Also post the output of the following command:
SELECT * FROM v$version;When you put some code or output please enclose it between two lines starting with {noformat}{noformat}
i.e.:
{noformat}{noformat}
SELECT ...
{noformat}{noformat}
Formatted code is easier to read.
Regards.
Al