INNER JOIN on three tables with condition - php

Question

I am trying to fetch all the photos detail from a tag slug (URL for the tag), the database has three tables:
|-----------------------|
|==> photo |
| -> id |
| -> custom_id |
| -> title |
|-----------------------|
|==> tags |
| -> id |
| -> slug |
|-----------------------|
|==> tags_relation |
| -> tid | <-- this is the tags.id
| -> pid | <-- this is the photo.custom_id
|-----------------------|
here is my mysql code to INNER JOIN all the tables and to get 20 photos from a tag:
SELECT photo.*, tags.*, tags_relation.*,
FROM tags WHERE tags.slug = 'people'
INNER JOIN tags_relation ON = tags_relation.tid = tags.id
INNER JOIN photo ON photo.custom_id = tags_relation.pid
LIMIT 20
ORDER BY photo.date DESC
The query is not correct anyway, and i can't understand how the INNER JOIN should work here, any idea?
Thanks

Answer 1

SQL has a specific ordering of clauses. In your case:
SELECT
FROM
WHERE
GROUP BY
ORDER BY
LIMIT
This is always the ordering within a query. Note that JOIN expressions are not "clauses". They are part of the FROM clause (and in MySQL, the update and delete clauses as well).
Applied to your query:
SELECT p.*, t.*, tr.*
FROM tags t INNER JOIN
tags_relation tr
ON tr.tid = t.id INNER JOIN
photo p
ON p.custom_id = tr.pid
WHERE t.slug = 'people'
ORDER BY p.date DESC
LIMIT 20
You will note that the indentation highlights the clauses which are a fundamental part of the language.
I also added table aliases, which make the query easier to write and to read. And fixed some minor things, such as misplaced commas.
I note you are pulling too many columns out of the data. You should just list the columns you want (probably p.*).

Answer 2

try this..
SELECT photo.*, tags.*, tags_relation.*
FROM tags WHERE tags.slug = 'people'
INNER JOIN tags_relation ON(tags_relation.tid = tags.id)
INNER JOIN photo ON (photo.custom_id = tags_relation.pid)
ORDER BY photo.date DESC
LIMIT 20