UNION ALL Query: Riddle

From: Pillai, Rajesh <Rajesh.Pillai_at_nordstrom.com>
Date: Tue, 27 Jan 2004 13:09:26 -0800
Message-ID: <F001.005DE36E.20040127130926@fatcity.com>

Hi All,

	The following query is giving different results in each run. I assure that no data modified between consecutive runs - 
	INSERT /* append parallel (z,8) */
	 INTO some_table 
	(SELECT /*parallel (a,8) */
            	a.item,
		a.loc,
		SUM(a.qty_type_1),
		SUM(a.qty_type_2)
	FROM
		(select  /*parallel (x,8) */
		      item,
		      loc,
		      qty_type_1,
		      to_number(NULL)		
		from
		      table_a x
		UNION ALL	
		select /*parallel (y,8) */
		      item,
		      loc,
		      to_number(NULL),
		      qty_type_2		
		from
		      table_b y
		) a
	GROUP BY
		a.item,
		a.loc);

Additional info -

Number of records in table_a and table_b is around 3M and 6M.

SQL> select * from v$version;

BANNER

---

Oracle8i Enterprise Edition Release 8.1.7.2.0 - Production PL/SQL Release 8.1.7.2.0 - Production
CORE 8.1.7.0.0 Production
TNS for Solaris: Version 8.1.7.2.0 - Production NLSRTL Version 3.4.1.0.0 - Production

I would appreciate any help in solving this mystery and all hints are welcome.

Thanks,
Rajesh Pillai

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Author: Pillai, Rajesh
  INET: Rajesh.Pillai_at_nordstrom.com

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