PostgreSQL comes with several data types, but users can create custom types to most faithfully represent any value. Data type management is mostly, but not exclusively, a developer's job, and data type design goes beyond the scope of this book. This is a quick recipe that covers only the simpler problem of the need to apply a specific change to an existing data type.
Enumerative data types are defined like this:
CREATE TYPE cookbook_author AS ENUM ('Hannu','Simon');
The other popular case is composite data types, which are created in this way:
CREATE TYPE node AS ( node_name text, connstr text, standbys text[]);
Say you are upgrading your database to edition, or version, 2.0 and you need a new value for the enumerative type that we defined in the preceding code. You want to put the new value in a certain position to preserve the alphabetical ordering. For that, you can use an ALTER TYPE syntax, like this:
ALTER TYPE cookbook_author...