So far in this book, you came across examples of creating new data types or user-defined types and operators. What we haven't discussed so far is how to index these types. In PostgreSQL, an index is more of a framework that can be extended or customized for using different strategies. In order to create new index access methods, we have to create an operator class. Let's take a look at a simple example.

Let's consider a scenario where you have to store some special data such as an ID or a social security number in the database. The number may contain non-numeric characters, so it is defined as a text type:

CREATE TABLE test_ssn (ssn text);
 
INSERT INTO test_ssn VALUES ('222-11-020878');
INSERT INTO test_ssn VALUES ('111-11-020978');

Let's assume that the correct order for this data is such that it should be sorted on the last six digits and not the ASCII value of the string.

The fact that these numbers need a unique sort order presents a challenge when it comes...