INDEXES - MIDTERM ADDBASE 3RD YEAR 1ST SEM

1. * Property of STI
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Indexes
F0004
What is an Index?
 An index is a data structure used in
database systems to perform faster
lookup.
 Indexes can greatly improve the
performance of searches on the
indexed column or columns.
 Example:
SELECT companyname
FROM supplier
WHERE supplierid = 'NBS'
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___________________ * Property of STI
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Indexes
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CREATE INDEX
 The syntax is shown below:
CREATE [UNIQUE] INDEX
<indexname> ON <table
name>(<column list>)
 This syntax creates an index on the
values of the attribute in <column
list> from table <table name>.
 Example:
CREATE UNIQUE INDEX
supplierindex ON
suppliers(supplierid);
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* Property of STI
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Indexes
F0004
When to Create an Index?
 Factors that can be considered to
determine if you should create an
index are as follows:
 Keys and unique columns
 Frequency of search
 Size of table
 Number of updates
 Space considerations
 Data distribution
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Indexes
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DROP INDEX
 The syntax is shown below:
DROP INDEX <index name>
 This syntax removes an index
specified by the <index name>.
 Example:
DROP INDEX supplierindex;
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2. * Property of STI
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Indexes
F0004
Composite Index
 A composite index is an index that
can contain one, two, or more
columns. The syntax is shown
below:
CREATE [UNIQUE] INDEX
<indexname> ON <table
name>(<column1>,
<column1>, …<columnN>)
 Example:
CREATE INDEX name
ON student (stud_lname,
stud_fname)
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* Property of STI
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Indexes
F0004
Composite Index
 In creating composite index, the
order of columns should be the
same as the order of the columns
in the table.
 Composite indexes are useful for
searching on all columns in the
index or on the first columns only.
 Example:
CREATE INDEX fname_lname
ON student stud_fname,
stud_lname;
CREATE INDEX lname_fname
ON student stud_lname,
stud_fname;
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