MYSQL - Split Data Into Multiple Rows

I have imported some data using an application that collects info from IMDB and transfers them into a MYSQL database.

It seems the fields have not been normalized and contained many values within 1 field

For example:

Table Movie
MovieID          Movie_Title           Written_By
1                Movie1                Person1, Person2   
2                Movie2                Person3  
3                Movie3                Person4, Person2, Person6  

Is there way to separate the values and have them inserted into another table to something like this and without any duplicates?

Table Writers
WriterID         Written_By                MovieId      
1                Person1                   1
2                Person2                   1
3                Person3                   3

I did some googling and found that I am supposed to process this data using PHP. But I have no knowle开发者_如何学Cdge with PHP at all.

Is there anyway to convert this data using just MYSQL?

You can use a stored procedure which uses a cursor to solve this but it's not very elegant but neither is a comma separated list of writers !

Had the following code lying around from a similar question but you'd better check it thoroughly.

Hope it helps :)

mysql> select * from movies_unf;
+---------+-------------+------------------------------------------------------+
| movieID | movie_title | written_by                                           |
+---------+-------------+------------------------------------------------------+
|       1 | movie1      | person1, person2                                     |
|       2 | movie2      | person3                                              |
|       3 | movie3      | person4, person2, person6                            |
|       4 | movie4      | person4, person4, person1, person2, person1,person8, |
|       5 | movie1      | person1, person2                                     |
+---------+-------------+------------------------------------------------------+
5 rows in set (0.00 sec)

call normalise_movies_unf();

mysql> select * from movies;
+----------+--------+
| movie_id | title  |
+----------+--------+
|        1 | movie1 |
|        2 | movie2 |
|        3 | movie3 |
|        4 | movie4 |
+----------+--------+
4 rows in set (0.00 sec)

mysql> select * from writers;
+-----------+---------+
| writer_id | name    |
+-----------+---------+
|         1 | person1 |
|         2 | person2 |
|         3 | person3 |
|         4 | person4 |
|         6 | person6 |
|        12 | person8 |
+-----------+---------+
6 rows in set (0.00 sec)

mysql> select * from movie_writers;
+----------+-----------+
| movie_id | writer_id |
+----------+-----------+
|        1 |         1 |
|        1 |         2 |
|        2 |         3 |
|        3 |         2 |
|        3 |         4 |
|        3 |         6 |
|        4 |         1 |
|        4 |         2 |
|        4 |         4 |
|        4 |        12 |
+----------+-----------+
10 rows in set (0.00 sec)

Example tables

drop table if exists movies_unf;
create table movies_unf
(
movieID int unsigned not null primary key,
movie_title varchar(255) not null,
written_by varchar(1024) not null
)engine=innodb;

insert into movies_unf values 
(1,'movie1','person1, person2'),
(2,'movie2','person3'),
(3,'movie3','person4, person2, person6'),
(4,'movie4','person4, person4, person1, person2, person1,person8,'), -- dodgy writers
(5,'movie1','person1, person2'); -- dodgy movie

drop table if exists movies;
create table movies
(
movie_id int unsigned not null auto_increment primary key,
title varchar(255) unique not null
)engine=innodb;

drop table if exists writers;
create table writers
(
writer_id int unsigned not null auto_increment primary key,
name varchar(255) unique not null
)engine=innodb;

drop table if exists movie_writers;
create table movie_writers
(
movie_id int unsigned not null,
writer_id int unsigned not null,
primary key (movie_id, writer_id)
)engine=innodb;

Stored procedure

drop procedure if exists normalise_movies_unf;

delimiter #

create procedure normalise_movies_unf()
begin

declare v_movieID int unsigned default 0;
declare v_movie_title varchar(255);
declare v_writers varchar(1024);

declare v_movie_id int unsigned default 0;
declare v_writer_id int unsigned default 0;
declare v_name varchar(255);

declare v_csv_done tinyint unsigned default 0;
declare v_csv_idx int unsigned default 0;

declare v_done tinyint default 0;
declare v_cursor cursor for 
    select distinct movieID, movie_title, written_by from movies_unf;

declare continue handler for not found set v_done = 1;

start transaction;

open v_cursor;
repeat
  fetch v_cursor into v_movieID, v_movie_title, v_writers;

  set v_movie_title = trim(v_movie_title);
  set v_writers = replace(v_writers,' ', '');

  -- insert the movie
  insert ignore into movies (title) values (v_movie_title);
  select movie_id into v_movie_id from movies where title = v_movie_title;  

  -- split the out the writers and insert
  set v_csv_done = 0;       
  set v_csv_idx = 1;

  while not v_csv_done do
    set v_name = substring(v_writers, v_csv_idx, 
      if(locate(',', v_writers, v_csv_idx) > 0, 
        locate(',', v_writers, v_csv_idx) - v_csv_idx, 
        length(v_writers)));

      set v_name = trim(v_name);

      if length(v_name) > 0 then
        set v_csv_idx = v_csv_idx + length(v_name) + 1;

        insert ignore into writers (name) values (v_name);
        select writer_id into v_writer_id from writers where name = v_name; 
        insert ignore into movie_writers (movie_id, writer_id) values (v_movie_id, v_writer_id);
      else
        set v_csv_done = 1;
      end if;

  end while;

until v_done end repeat;
close v_cursor;

commit;

truncate table movies_unf;

end#

delimiter ;

EDIT

Amended sproc so that it doesnt skip key values !

drop procedure if exists normalise_movies_unf;

delimiter #

create procedure normalise_movies_unf()
begin

declare v_movieID int unsigned default 0;
declare v_movie_title varchar(255);
declare v_writers varchar(1024);

declare v_movie_id int unsigned default 0;
declare v_writer_id int unsigned default 0;
declare v_name varchar(255);

declare v_csv_done tinyint unsigned default 0;
declare v_csv_idx int unsigned default 0;

declare v_done tinyint default 0;
declare v_cursor cursor for 
    select distinct movieID, movie_title, written_by from movies_unf;

declare continue handler for not found set v_done = 1;

start transaction;

open v_cursor;
repeat
  fetch v_cursor into v_movieID, v_movie_title, v_writers;

  set v_movie_title = trim(v_movie_title);
  set v_writers = replace(v_writers,' ', '');

  -- insert the movie

  if not exists (select 1 from movies where title = v_movie_title) then
    insert ignore into movies (title) values (v_movie_title);
  end if;  
  select movie_id into v_movie_id from movies where title = v_movie_title;  

  -- split the out the writers and insert
  set v_csv_done = 0;       
  set v_csv_idx = 1;

  while not v_csv_done do
    set v_name = substring(v_writers, v_csv_idx, 
      if(locate(',', v_writers, v_csv_idx) > 0, 
        locate(',', v_writers, v_csv_idx) - v_csv_idx, 
        length(v_writers)));

      set v_name = trim(v_name);

      if length(v_name) > 0 then
        set v_csv_idx = v_csv_idx + length(v_name) + 1;


        if not exists (select 1 from writers where name = v_name) then
          insert ignore into writers (name) values (v_name);
        end if;
        select writer_id into v_writer_id from writers where name = v_name; 
        insert ignore into movie_writers (movie_id, writer_id) values (v_movie_id, v_writer_id);
      else
        set v_csv_done = 1;
      end if;

  end while;

until v_done end repeat;
close v_cursor;

commit;

truncate table movies_unf;

end#

delimiter ;

MySQL's not particularly good for string manipulation of this sort. You'd most likely find it much easier to round-trip the data through a regular programming language (perl, php, ruby, python, etc...) which have far more robust text-mungeing functions.

And you'd most likely want to view the results before doing anything irreversable, especially if the names might have embedded commas.

Alice,Eve,Bob

is easy to split on the comma, but what about

Alice,Eve,Esquire.,Bob

Unfortunately, there is no string splitting function in MySQL. Here's a related post (not quite a duplicate of yours) with a solution that splits a string into multiple columns.