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UNION ALL slow (cost goes from 75 and 173 to 450,789!)

761812Jun 14 2010 — edited Jun 14 2010

Hi,

I have two Selects (lots of joins - big tables)

Select A) has an explain plan cost of 75
Select B) has an explain plan cost of 173

If I union (or union all) the cost goes up to 450,789!

I can paste in the queries, plans etc - but if anyone has any quick ideas that'd be great.

Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bi

What I'd like is to force the optomiser to run each query sequentially - but not really sure how.

Any help would be really appreciated - I have few hairs left and am just about to tear the last one out!

Cheers,
Patrick

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Locked on Jul 12 2010

Added on Jun 14 2010

#oracle, #performance, #sql

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