Oracle performance issue with "UNION ALL" in 10g
just assume that
SQL Query :
SQL1 UNION ALL SQL2
separately exection times are
SQL1 -- 5 seconds (total count - 5,00000)
SQL2 -- 10 seconds (total count - 4,00000)
if I use UNION ALL. it takes 30 minutes to complete the execution.why it takes that much time if I use UNION ALL.?
look at what, you haven;t posted anything to look at
is therey anyway to improve performance of that query ? if we use UNION ALL it takes much time. do we need to use any hints or any other function?
what query, you havent posted anything
no execution plan
posting stuff in different colours doesnt make it less true
Trace the three executions, compare execution plans as well as buffer_gets.
Originally Posted by victoryhendry
Pablo (Paul) Berzukov
Author of Understanding Database Administration
available at amazon and other bookstores.
Disclaimer: Advice is provided to the best of my knowledge but no implicit or explicit warranties are provided. Since the advisor explicitly encourages testing any and all suggestions on a test non-production environment advisor should not held liable or responsible for any actions taken based on the given advice.
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