新知识点1：10GR2 HASH GROUP BY BUG
BUG 描述：
This problem is introduced in the 10.2.0.1 base release.

Wrong results possible from the result of a non-distinct aggregation
with a group by (such as sum(col)) when HASH GROUP BY is used.
The wrong results show as missing values from the aggregate.

Workaround:
Increase the memory used by hash group by
or
Disable the use of hash group by
eg: set optimizer_features_enable to "10.1.0"
or
set "_gby_hash_aggregation_enabled" to FALSE.
Versions confirmed as being affected 10.2.0.1
10.2.0.2

This issue is fixed in 10.2.0.3 (Server Patch Set)
11g (Future version)

ITPub博客

2012-01-06 10gR2 HASH GROUP BY BUG

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