From10Gr2, HASH UNIQUE Operation Returns Results in UNSORTED ORDER by Default
(Doc ID 341838.1)
Last updated on SEPTEMBER 15, 2016
Oracle Server - Enterprise Edition - Version: 10.2.0.1 to 188.8.131.52
This problem can occur on any platform.
From 10gR2, executing SELECT DISTINCT with default options may not utilise a SORT UNIQUE, rather a HASH UNIQUE may be used causing results to be returned in UNSORTED order.
Setting optimizer_features_enable="9.2.0" reverts to the previous behavior:
SQL> alter session set optimizer_features_enable="9.2.0";
Upgrade and earlier release to 10g Release 2 and above.
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