Question

I have a item table, a tags table and a item_tagged table.

I want to remove rows from the the database if an item is not found in an array.

For example:

$array = 'john', 'game', 'nintendo';

Item id 2 has the following tags in the database:

'john', 'game', 'wonderful'

So ‘wonderful’ should be removed from the database.

What would be the sql for this?

item: id, content

item_tagged: item_id, tag_id

tag: id, name

Answer 1

Assuming you want to keep only the tags in the array, this should do the job.

DELETE FROM item_tagged 
  WHERE item_id = 2 AND tag_id NOT IN (
    SELECT id FROM tag WHERE name IN (<<list your array contents here>>)
  )
;

Keep in mind this will not delete any orphaned tags, eg tags which are not assigned to any item.