The document discusses database indexing and different types of indexes. It defines indexing as optimizing database performance by minimizing disk accesses during queries. Primary indexes are defined on ordered data files ordered by a key field, usually the primary key. Secondary indexes can be on candidate keys or non-key fields. Indexes can also be clustered or ordered on non-key fields, and can be dense indexes with an entry for every search key, or sparse indexes with one entry per data block.

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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.