07 ohp slide handout 1 - INDEXES
0 likes195 views
An index is a data structure used to perform faster lookups in a database. Indexes can improve the performance of searches on indexed columns. Factors like keys, search frequency, table size, and updates determine when to create an index. The CREATE INDEX syntax creates an index on specified columns, while DROP INDEX removes an index. Composite indexes contain multiple columns and support searches on all or leading columns in the specified order.
![* Property of STI
Page 1 of 6
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'
1 _________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________ * Property of STI
Page 3 of 6
Indexes
F0004
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);
3 __________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
* Property of STI
Page 2 of 6
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
2 _________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________ * Property of STI
Page 4 of 6
Indexes
F0004
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;
4 __________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________](https://image.slidesharecdn.com/07ohpslidehandout1-150820122238-lva1-app6892/85/07-ohp-slide-handout-1-INDEXES-1-320.jpg)
![* Property of STI
Page 5 of 6
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)
5 _________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
* Property of STI
Page 6 of 6
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;
6 _________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________](https://image.slidesharecdn.com/07ohpslidehandout1-150820122238-lva1-app6892/85/07-ohp-slide-handout-1-INDEXES-2-320.jpg)
07 ohp slide handout 1 - INDEXES
- 1. * Property of STI Page 1 of 6 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' 1 _________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ * Property of STI Page 3 of 6 Indexes F0004 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); 3 __________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ * Property of STI Page 2 of 6 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 2 _________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ * Property of STI Page 4 of 6 Indexes F0004 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; 4 __________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________
- 2. * Property of STI Page 5 of 6 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) 5 _________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ * Property of STI Page 6 of 6 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; 6 _________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________