Optimizing SQLPertemuan 13

Matakuliah : T0413/Current Popular IT IITahun : 2007

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Learning Outcomes

Pada akhir pertemuan ini, diharapkan mahasiswa akan mampu mendemonstrasikan proses optimasi di dalam SQL

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Outline Materi

• Using indexes• Types of indexes• Reprashing queries

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USING INDEX

One of important ways to improve systemPerformance

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SEVERAL WAYS TO CATEGORIZE INDEXES

• UNIQUE• NON UNIQUE

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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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TYPE OF INDEXS • B+ trees• Join indexes & clusters• Bitmap indexes• R-trees

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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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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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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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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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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)