Question

I have a comma separated list of numbers in a MySQL entry ‘id_user’ like so:

127,130,150,12,4,7,8,9

What is the best way to find a number in this comma-separated list and (1) remove it with the comma if it’s with other numbers or (2) just remove itself if the number is by itself like:

127

Then update the MySQL entry.

So if I wanted to remove 150 from the list, it would be updated in the MySQL as:

127,130,12,4,7,8,9

I want to avoid trying to remove the id ’12’ but end up removing the ’12’s in numbers like 127 or 512

Thank you!

Answer 1

Reading between the lines, it sounds to me like you are storing a list of foreign keys in a comma-separated string field to represent a many-to-many relationship. This is not a good idea.

What you should do instead is create a table to store the relations.

For example, lets say you have a table called users and you want to store friend relationships between them. What you are doing is something like this (N.B. I realised this is actually not a great example as I wrote the end but I’m sticking with it for now):

  id  |  name  |  friends
------+--------+-----------
  1   | Dave   |  2,4
  2   | Bob    |  1
  3   | Tom    |  4
  4   | Bill   |  1,3

Whereas what it’s much better to do is something like this:

users

  id  |  name  
------+--------
  1   | Dave   
  2   | Bob   
  3   | Tom    
  4   | Bill   

friends

  id  |  user  |  friend
------+--------+----------
  1   |   1    |    2
  2   |   1    |    4
  3   |   2    |    1
  4   |   3    |    4
  5   |   4    |    1
  6   |   4    |    3

To select Dave’s friends you can do

SELECT u.*
FROM friends f
JOIN users u ON u.id = f.friend
WHERE f.user = 1

…and to delete the relationship between Dave and Bob (what you want to do here), you can simply do

DELETE FROM friends
WHERE (
  user = 1 AND friend = 2
) OR (
  user = 2 AND friend = 1
)