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What are the factors you will check for the performane
optimization for a database query?
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Answer Posted / samba shiva reddy . m
1.In the select statement give which ever the columns you need
don't give select * from
2.Do not use count()function
3.use indexes and drop indexes regularly it B tree structure we are not going to drop means it will take time for creating indexes it self.
4.when joining the tables use the id's(integer type)not string
5.Sometimes you may have more than one subqueries in your main query. Try to minimize the number of subquery block in your query.
6.Use operator EXISTS, IN and table joins appropriately in your query.
a) Usually IN has the slowest performance.
b) IN is efficient when most of the filter criteria is in the sub-query.
c) EXISTS is efficient when most of the filter criteria is in the main query.
7.Use EXISTS instead of DISTINCT when using joins which involves tables having one-to-many relationship.
8.Try to use UNION ALL in place of UNION.
9.Avoid the 'like' and notlike in where clause.
10.Use non-column expression on one side of the query because it will be processed earlier.
11.To store large binary objects, first place them in the file system and add the file path in the database.
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