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7.8

Optimize a query....

Asked by imarshad in Oracle Database

Tags: oracle, optimize, query

Hi all,
         I am in process of converting a database from Access to Oracle 9i....  I have used the following query to select latest records (with max.DateTime) of units from a table.....The table contains about 0.5 million records. Table name is VData and the field of interest is DateTime which is varchar of the format "YYYY/MM/DD HH:MM"

Select * from VData where UnitID = 1000 and DateTime= (Select Max(DateTime) from VData where UnitID = 1000)
and also a slight variation
Select * from (Select * from VData where UnitID = 1000 Order By DateTime DESC) where rownum=1;

These work perfectly well in MS ACCESS. I loop through UnitID's (from 1000 to 1150) using this query i.e this query is called 150 times in a loop and I get the result within 2-3 seconds. Now that I have converted my database to Oracle(Same no. of records) and it takes about 12-13 seconds for this query to execute. This is way too unacceptable. Oracle should be faster then Access or ????? I have the same indexes on both databases (i.e in Access and Oracle). What should I do to reduce the time taken by the query??? Any optimization or better way of doing it ......

Imran
 
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[+][-]02/07/06 02:01 AM, ID: 15890676Accepted Solution

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Zone: Oracle Database
Tags: oracle, optimize, query
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Solution Provided By: schwertner
Participating Experts: 3
Solution Grade: B
 
[+][-]02/07/06 03:13 AM, ID: 15890988Author Comment

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