Introduction
Defining columns with UNIQUE
Adding and removing UNIQUE constraints
Instruction
Excellent work! Now, let's try to do the opposite: delete a constraint from an existing table. Here's the table:
CREATE TABLE group_game ( id integer PRIMARY KEY, name varchar(64) UNIQUE, min_players integer, max_players integer );
There's a UNIQUE constraint on the name column. To remove it, we can use this code:
ALTER TABLE group_game DROP CONSTRAINT group_game_name_key;
How do we know the name of the constraint? PostgreSQL's naming convention for UNIQUE is table_name + _ + constraint_column(s) + _ + key. That's why our constraint was named group_game_name_key.
Exercise
After the previous exercise, we've got the new UNIQUE constraint in our table card_game:
CREATE TABLE card_game ( id integer PRIMARY KEY, name varchar(64) UNIQUE, card_game_rank integer UNIQUE );
However, you now need to get rid of the UNIQUE constraint on the name column.
