optimizing sql pertemuan 13 matakuliah: t0413/current popular it ii tahun: 2007
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Optimizing SQLPertemuan 13
Matakuliah : T0413/Current Popular IT IITahun : 2007
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Bina Nusantara
Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa akan mampu mendemonstrasikan proses optimasi di dalam SQL
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Bina Nusantara
Outline Materi
• Using indexes• Types of indexes• Reprashing queries
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Bina Nusantara
USING INDEX
One of important ways to improve systemPerformance
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Bina Nusantara
SEVERAL WAYS TO CATEGORIZE INDEXES
• UNIQUE• NON UNIQUE
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Bina Nusantara
CREATE INDEX• SINTAX :
CREATE [UNIQUE] INDEX index-Name ON table-Name ( Simple-column-Name [ ASC | DESC ] [ , Simple-column-Name [ ASC | DESC ]] * )
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Bina Nusantara
TYPE OF INDEXS • B+ trees• Join indexes & clusters• Bitmap indexes• R-trees
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Bina Nusantara
REPHRASING QUERIES• Optimizer in the DBMS is supposed to convert
queries to the most efficient formulation and execution
• Two general flavors of optimizer– Rule based– Cost based
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Bina Nusantara
REPHRASING QUERIES• Here are some rules of thumb to make queries
run faster :1. Be careful about using value expressions or datatype
conversions on indexed values used in predicates2. The same applies to <> (does not equal)
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Bina Nusantara
REPHRASING QUERIES (Cont.)3. ANY and EXISTS
4. Place the predicates that are likely to eliminate the most rows from the output first in where clause
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Bina Nusantara
REPHRASING QUERIES (Cont.)5. LEFT and RIGHT OUTER joins are interconvertible.
LEFT joins may be faster6. In a join, place the table with fewer rows first in the
FROM clause.7. With an indexes column referenced in a predicate,
you may do a bit better by combining equalities and inequalities
(x>=8 lebih cepat daripada x>7)8. NULLs value
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Bina Nusantara
REPHRASING QUERIES (Cont.)9. If we want more than 20 percent rows of table
better off without using an index10. If we refferencing a multi column index, you
need not reference the query every column11. Avoid using like12. Often a UNION of two queries will do better than
a single query (using OR)