Inversion List

An inversion list is part of an index. An inversion list consists of a secondary key and the related primary key(s).

A table contains the names of all customers in a hotel. You have defined the primary key for this table as the customer number cno.

cno

surname

firstname

2003

Miller

Frank

2011

Griffith

Mary

2078

Miller

Jane

2104

Miller

Susan

2295

Miller

Sally

Now define an index for the surname column. The surname column now becomes an indexed column (also known as an inverted column).

The index contains the following inversion lists:

Ў        an inversion list with the secondary key Griffith and the primary key 2011 (the surname Griffith only appears once in the table)

Ў        a further inversion list with the secondary key Miller and the primary keys 2003, 2078, 2104, and 2295 (the surname Miller appears four times in the table)