PostgreSQL Guide

Database Design

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> How can I restrict the possible values for a column?

You have two options:

1. A CHECK CONSTRAINT:

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

2. A ENUM:

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

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

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