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So, I'm creating a database for one of my classes using pg admin. I got all the data in no problem but my one issue is this one error that I don't really understand.

ERROR: duplicate key value violates unique contraint "movies_pkey"

DETAIL: key(movie_num)=20 already exists 

The above is the error I am getting.

-- DROP'ping tables clear out any existing data

DROP TABLE IF EXISTS movies;

DROP TABLE IF EXISTS actors;



-- CREATE the table, note that id has to be unique, and you must have a name

CREATE TABLE actors(

    id INTEGER PRIMARY KEY,

    name VARCHAR(20) NOT  NULL

);



INSERT INTO actors(id, name) VALUES(

    1,

    'Sean Connery');

INSERT INTO actors(id, name) VALUES(

    2,

    'George Lazenby');

INSERT INTO actors(id, name) VALUES(

    3,

    'Roger Moore');

INSERT INTO actors(id, name) VALUES(

    4,

    'Timothy Dalton');

INSERT INTO actors(id, name) VALUES(

    5,

    'Pierce Brosnan');



INSERT INTO actors(id, name) VALUES(

    6,

    'Daniel Craig');





-- CREATE the table, note movie_num is unique and title and year are required fields, though the actor can be optionally empty

CREATE TABLE movies(

    movie_num INTEGER PRIMARY KEY,

    title VARCHAR(35) NOT NULL,

    actor INTEGER,

    year INTEGER NOT NULL

);



INSERT INTO movies(movie_num, title, actor, year) 

VALUES(

    2,

    'From Russia With Love',

    1,

    1963);

INSERT INTO movies(movie_num, title, actor, year)

VALUES(

    3,

    'Goldfinger',

    1,

    1964);

INSERT INTO movies(movie_num, title, actor, year) VALUES(

    4,

    'Thunderball',

    1,

    1965);

INSERT INTO movies(movie_num, title, actor, year) VALUES(

    5,

    'You Only Live Twice',

    1,

    1967);

INSERT INTO movies(movie_num, title, actor, year) VALUES(

    6,

    'On Her Majesty''s Secret Service',

    2,

    1969);

INSERT INTO movies(movie_num, title, actor, year) VALUES(

    7,

    'Diamonds Are Forever',

    1,

    1971);

INSERT INTO movies(movie_num, title, actor, year) VALUES(

    8,

    'Live and Let Die',

    3,

    1973);

INSERT INTO movies(movie_num, title, actor, year) VALUES(

    9,

    'The Man With The Golden Gun',

    3,

    1974);

INSERT INTO movies(movie_num, title, actor, year) VALUES(

    10,

    'The Spy Who Loved Me',

    3,

    1977);

INSERT INTO movies(movie_num, title, actor, year) VALUES(

    11,

    'Moonraker',

    3,

    1979);

INSERT INTO movies(movie_num, title, actor, year) VALUES(

    12,

    'For Your Eyes Only',

    3,

    1981);

INSERT INTO movies(movie_num, title, actor, year) VALUES(

    14,

    'A View To A Kill',

    3,

    1985);

INSERT INTO movies(movie_num, title, actor, year) VALUES(

    15,

    'The Living Daylights',

    4,

    1987);

INSERT INTO movies(movie_num, title, actor, year) VALUES(

    16,

    'License To Kill',

    4,

    1989);

INSERT INTO movies(movie_num, title, actor, year) VALUES(

    18,

    'Tomorrow Never Dies',

    5,

    1997);

INSERT INTO movies(movie_num, title, actor, year) VALUES(

    20,

    'Die Another Day',

    5,

    2003);

INSERT INTO movies(movie_num, title, actor, year) VALUES(

    1,

    'Dr. No',

    1,

    1962);

INSERT INTO movies(movie_num, title, actor, year) VALUES(

    13,

    'Octopussy',

    3,

    1983);

INSERT INTO movies(movie_num, title, actor, year) VALUES(

    17,

    'Goldeneye',

    5,

    1995);

INSERT INTO movies(movie_num, title, actor, year) VALUES(

    19,

    'The World Is Not Enough',

    5,

    1999);

INSERT INTO movies(movie_num, title, actor, year) VALUES(

    20,

    'Casino Royale',

    6,

    2006);

INSERT INTO movies(movie_num, title, actor, year) VALUES(

    21,

    'Quantum of Solace',

    6,

    2008);

INSERT INTO movies(movie_num, title, actor, year) VALUES(

    22,

    'Skyfall',

    6,

    2012);

INSERT INTO movies(movie_num, title, actor, year) VALUES(

    23,

    'Spectre',

    6,

    2015);

And this is the database I created.

Any help is much appreciated.