Let’s say we have a bank. Our bank wants to give each account for each user a unique name, for instance, “Personal” or “Checking.” How can we make sure each account has a unique name for each user?

Add unique constraint when create a new table:

CREATE TABLE directors (  id SERIAL PRIMARY KEY,  name VARCHAR(100) UNIQUE NOT NULL    )

Change existing table, modify one field to be unique:

ALTER TABLE directors ADD CONSTRAINT directors_name_unique UNIQUE(name)

So now if we trying to insert the duplicate rows it will report error:

INSERT INTO directors (name) VALUES (‘Quintin Tarantino‘), (‘Quintin Tarantino‘) ;

Sometime, the unique constraint can be a combination of mulit fields:

ALTER TABLE movies ADD CONSTRAINT unique_title_and_release UNIQUE(title, release-date)

[PostgreSQL] Ensure Uniqueness in Postgres