shistorian=> create type occurrence_type as enum ('modbus-read', 'user click');
CREATE TYPE

shistorian=> create table things (id serial, name varchar, what occurrence_type);
CREATE TABLE

shistorian=> insert into things values (1, 'uh oh', 'user click');
INSERT 0 1

shistorian=> select * from things;
 id | name  |    what
----+-------+------------
  1 | uh oh | user click
(1 row)

shistorian=> insert into things values (2, 'yay', 'modbus-read');
INSERT 0 1
shistorian=> select * from things;
 id | name  |    what
----+-------+-------------
  1 | uh oh | user click
  2 | yay   | modbus-read
(2 rows)

shistorian=> insert into things values (2, 'yay', 'modbus-read22222');
ERROR:  invalid input value for enum occurrence_type: "modbus-read22222"
LINE 1: insert into things values (2, 'yay', 'modbus-read22222');