| How Oracle Read blocks [message #289717] |
Tue, 25 December 2007 21:20  |
lzfhope
Messages: 69
Registered: July 2006
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Member |
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hi,
In a windows os system,How oracle Read Blocks of a table?
Given a sql like this : "select * from Test_Table" .Test_Table is a table object .
Suppose that ,the table test_table has 10 extents and each extent has 10 blocks .Which order will the oracle use to read this blocks?
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| Re: How Oracle Read blocks [message #289748 is a reply to message #289720] |
Wed, 26 December 2007 00:30  |
lzfhope
Messages: 69
Registered: July 2006
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Member |
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Under greatly parts of circumstances,i do not care the orders,
But,sometimes this decides order of the query result .
Assume the table has records like these below:
1 ,100
2 ,300
3 ,400
4 ,600
.....
n ,n*100
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I want that the output will list in order.So the order of reading blocks is important.
Maybe ,somebody say why not using "order by".Yeah,Using the "order by" clause , the oracle will produce the necessary result. But ,I do not want to use the "order by" clause ,neithor the sorted index.
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| Re: How Oracle Read blocks [message #289762 is a reply to message #289748] |
Wed, 26 December 2007 01:20 |
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Michel Cadot
Messages: 68686
Registered: March 2007
Location: Nanterre, France, http://...
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Senior Member
Account Moderator |
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THE ONLY WAY TO GET A SPECIFIC ORDER IS TO USE "ORDER BY" CLAUSE.
This is a definitive rule.
I already posted examples that show that extents may be read in random fashion.
Regards
Michel
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