an index which is created other than index based on primary key, to speed up processing.
Indexing of secondary keys can only be done when the key is ordered. An index file stores the position of the record a particular category.
In this example, a secondary key is ordered alphabetically, the first record which starts with b is #14, the first record which starts with c is #26
Index file: Database:
Category | Start position ID | First_name
---------|--------------- ---|-----------
a | 1 1 | Aaron
b | 14 2 | Abe
c | 26 ...
d | 34 14 | Barry
A query run on the data will be much faster, instead of looking at every record, the program can skip to start position of the category for the first letter of their name. For example, if this query was run:
SELECT First_name
FROM database
WHERE First_name = "Bryan"
The program would search for barry between records 14 - 25 rather than looking at all the records in the database.
