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Dr Ramadan Babers
Faculty of Science - Helwan University
Fall-2018
D B
LEC-8

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Indexing
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3. Introduction
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 we need to check all First_Name (Table full scan)
(if equal not equal “Ibrahim”)
 If we have 1,000,000 records & we can check 10,000 per
second
 So, we will need 100 seconds to get the result of pervious
select statement.
 Indexing mechanisms used to speed up access to
desired data.

4. Introduction
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Indexing mechanisms used to speed up access to desired data.

5. Indexing
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 Indexing is a way to optimize performance of a
database by minimizing the number of disk accesses
required when a query is processed.
 An index or database index is a data structure which
is used to quickly locate and access the data in a
database table.

6. Indexing
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 We know that data is stored in the form of records.
 Every record has a key field, which helps it to be
recognized uniquely.

7. Indexing Types
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Indexing is defined based on its indexing attributes. Indexing can be of
the following types:
 Primary Index: Primary index is defined on an ordered data file.
The data file is ordered on a key field. The key field is generally
the primary key of the relation.
 Secondary Index: Secondary index may be generated from a
field which is a candidate key and has a unique value in every
record, or a non-key with duplicate values.
 Clustering Index: Clustering index is defined on an ordered data
file. The data file is ordered on a non-key field.

8. Ordered Indexing Types (non-key field)
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Ordered Indexing is of two types:
1- Dense Index
2- Sparse Index

9. Dense Index
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• In dense index, there is an index record for every search
key value in the database.
• This makes searching faster but requires more space to
store index records itself.
• Index records contain search key value and a pointer to
the actual record on the disk.

10. Sparse Index
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• One index entry for each
block
• To search a record, we
first proceed by index
record and reach at the
actual location of the data.
• If the data we are looking
for is not where we
directly reach by
following the index, then
the system starts
sequential search until the
desired data is found.