Why am I getting ERROR: duplicate key value violates unique constraint "movies_pkey'
You cannot have duplicate keys on primary key column i.e movie_num=20
 Change Movie Die Another Day with movie_num =20 to 24 

   -- 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(
        24,
        'Die Another Day',
        5,
        2003);  -- changed movie_num from 20 to 24*/
    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);