Question

If I have a tag system like Stackoverflow. I can add tags, save and after delete a tag, or add new tags.

For example, initially:

PHP, JQUERY, ARRAYS

save question and publish,

I changed my mind, and I will delete JQUERY, so I edited my question to only two tags:

PHP, ARRAYS

My question is: what is the best way to remove the tag from database after inserted?
I need to check which tag is removed.

Any idea? Thanks!

To clarify the problem:

i have a many- to -many table

$first = array (php, jquery, arrays)

question1 | php
question1 | jquery
question1 | arrays

after edited, i will have (the goal):

$first = array (php, jquery)

question1 | php
question1 | jquery

to add new tags is easy. Unique constrain, and a foreach solves the problem.
But to remove tags. I need to remove the specific tag arrays from the junction table.

the question is how ?

so, i have this array: $first = array (php, jquery)

and this table structure (THIS IS THE PROBLEM):

question1 | php
question1 | jquery
question1 | arrays

Answer 1

This is best implemented as a many-to-many relationship.

You do this by using a junction table. For example

QUESTION
========
id, -- primary key
whatever

TAG
===
id, -- primary key
tag -- probably best with UNIQUE constraint

QUESTION_TAG
============
question_id, -- composite primary key, foreign key references QUESTION (id)
tag_id -- composite primary key, foreign key references TAG (id)

To remove a tag for a question, simply delete the record from the QUESTION_TAG table, eg

DELETE FROM `QUESTION_TAG`
WHERE `question_id` = :question_id
AND `tag_id` = :tag_id

Update

Your best bet is to make tag removal a capture-able event. What I mean by this is that each removal is handled in a way so you are able to capture the tag to be removed.

Another approach is to remove all QUESTION_TAG entries for the question and re-insert the tags to keep.