Question

I was wondering if I allowed my users to pick which categories their post will be displayed in and they can pick multiple categories from one to many.

• How would I store the categories id value or values in the database?
• Should I group each value together for example, 45,12,45,78 or should I store one value at a time?
• And how would my table structure look like?
• Or should I add it to an existing table?

Answer 1

The structure you are describing is really a many-to-many relationship (used in all tag-structures and alike).

Entries Table
+----+-------+------+
| id | title | text |
+----+-------+------+

Entries-to-Tags Table
+----------+--------+
| entry_id | tag_id |
+----------+--------+

Tags Table
+----+-----+
| id | tag |
+----+-----+

---

A typical SQL call to check on ALL entries from a tag would be

SELECT *
FROM tags_table as tg
LEFT JOIN entries_to_tags AS entg ON tg.id = entg.tag_id
LEFT JOIN entries AS en ON entg.entry_id = en.id
WHERE tg.tag = 'my tag'

A typical SQL call to check on tags from an entry would be

SELECT *
FROM entries AS en
LEFT JOIN entries_to_tags AS entg ON en.id = entg.entry_id 
LEFT JOIN tags_table AS tg ON entg.tag_id = tg.id
WHERE en.title = 'my article title'