标准化表格的简单方法

Question

I have a table like this -this is a part of users table which is getting update with more rows when a user is registering :

user_id languages 
1       english, french 
2       english,german,french
3       german
4       english, spanish

and in order to do a littel search I'm intrested of transforming this table into:

user_id language
1          english
1          french
2          english
2          german
2          french
3          german
4          english
4          spanish

Comment : not creating a new table but just right the correct select query from users table to do that. I'm using mysql with phpmyadmin. Any help will be welcome. Thank's.

Answer 1

As others have stated, storing comma-separated values in a column will cause you all sorts of pain over time. Having said that...

Create a numbers table (one way to do that is described here ). Once you have that, you can use it to split your comma-separated values onto separate rows:

select lang.user_id,
       SUBSTRING_INDEX(SUBSTRING_INDEX(lang.languages, ', ', numbers.n), ', ', -1) language
from numbers 
inner join lang on CHAR_LENGTH(lang.languages) - CHAR_LENGTH(REPLACE(lang.languages, ', ', ' ')) >= numbers.n - 1
order by lang.user_id, numbers.n;

DEMO