Question

I have a table in mysql:

user_item_text
    username, item, text

I want to normalize the data into three tables:

users
    user_id, username

items
    item_id, item_name

text
    text_id, text_name

How can I use the existing user_item_text table to create the three tables as described? There are around 800000 records.

Answer 1

Here is the example how to handle one table “user”:

create table users(
   user_id int not null auto_increment, 
   username varchar(50), 
   primary key(user_id), 
   index ind_user_username(username)
) engine = XXX;

insert into users(username) select distinct username from user_item_text

alter table user_item_text add user_id integer null

update user_item_text uit join users u on uit.username = u.username
set uit.user_id = u.user_id

alter table user_item_text drop column username

maybe you will be need to add the following steps before runing the last update:

1. adding index on user_item_text.username field to make update run faster
2. unique index on users.username instead of ordinary index
3. user_item_index.user_id should have FK

Hope it helps.

ps. i didn’t test query. They just showing you general approach.