Query Optimization
https://www.computersprofessor.com/2016/07/query-optimization.html
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Query optimization :
Query optimization is
the central activity during the passing phases in query.
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In this phase the DBMS most choose
what incidences to use, how to perform join operation what tables to use first
& so on.
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Each DBMS has its own algorithm for
determining the most efficient way to access the data.
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The query optimizer can be operate
in one of two models
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1.
Rule based optimizer :
It
uses present rules and points to determine the approach to execute a query.
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2.Cost based optimizer :
It use some
optimizer based on statistics about the object being accessed to determine the
best approach to execute query. In this case the optimizer process adds
processing cost the I/o cost & the resource cost (RAM & memory)
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