In Postgres, how do you restrict possible values for a particular column?

Question

I want to create a column element_type in a table (called discussion) that allows the text values \"lesson\" or \"quiz\" but will generate an error if

Answer 1

You could add a CHECK CONSTRAINT:

ALTER TABLE distributors 
   ADD CONSTRAINT check_types 
   CHECK (element_type = 'lesson' OR element_type = 'quiz');

Although IMO the cleaner option would be to create an ENUM:

CREATE TYPE element_type AS ENUM ('lesson', 'quiz');