Question

I have a SQL table, which looks like this:

id_question (int) | tags (varchar)
where “tags” field is
– either empty : NULL
– or is filled with one value (Ex: 1) (not numeric)
– or is filled with several comma separated values (ex: 273,2308,24) (not numeric)

id_question (int) | tags (varchar)
1 | 1,373
2 | 283,4555,308,12
3 | 283,25,3

ANd i have a blacklisted_tags array.
I would like to retrieve id_questions of all questions whose tags field do not have a blacklisted $tags_blacklist value.

For example:
$tags_blacklist = array (1,3)
=> I should get 2
and not 1 because it has 1 in its tags field
and not 3 because it has 3 in its tags field.

What should my SQL query look like?

Answer 1

your database design violates law of normalization #1: NEVER STORE COMMA-SEPARATED LISTS.

What you should have instead is this:

• id | tag
• 1 | 1
• 1 | 373
• 2 | 283
• 2 | 4555
• 2 | 308

etc.

This way your query becomes as easy as

SELECT DISTINCT id 
FROM YourTable
WHERE tag NOT IN (1, 3)