Data Indexing
Index: a data structure used to speed up selections on data records based on some attributes
Example: Index on ‘age’ attribute of Employee table.
age is a search key
An index consists of data entries that point to some raw data records
<key_value, data_pointer>
data_pointer raw data
Cost of calling pointer to raw data is constant e.g. 1 page I/O
Type of Indexes:
1) Tree-based
2) Hash-based
3) Bitmap-based
Primary Index vs. Secondary Index
Primary: uses the key attribute of a relation as the search key
Example: an index based on SSN of Employee table
Secondary: search key is NOT the key attribute
Example: an index based on ‘age’ of Employee
Clustered vs. un-clustered index
If the order of data records in file is the same as the order of data entries in the index, that index
is called CLUSTERED.
Index
interface b/w ______________________________________________________
raw data
There can only be ONE clustered index
a
0
p
0
a
1
p
1
a
0
a
1
….
a
n
-
1
a
n
