mysql query select by tag - mysql

Question

I have a database with 3 tables with content and i need to get content out of it based on a query of tags.
The tables look like this:
nv_entries:
id - title - year - etc..
nv_tags:
id - entrieid - tag
nv_images:
id - entrieid - source
Let's say i want all entries that have the tag 'rousseau' and both 'fuzz' in it.
After that the images should join aswell where entrieid = entrieid.
This can probably done with one query but i have no idea how.
$query = "SELECT * from nv_entries WHERE ???
please help

Answer 1

Since you have a one to many relationship between entries and tags, you have to use a pivot table on the tags table. Simply saying where tag = 'x" and tag = 'y" won't work because the engine looks at this on a row by row basis so tag can't have both values at the same time. So basically you pivot, assigning flags to each entry that state whether that entry has been seen to have the tag value you're looking for.
SELECT *
FROM nv_entries entries
JOIN (
SELECT entrieid,
COUNT(CASE WHEN (tag = 'rousseau') THEN 1 ELSE null END) has_rousseau,
COUNT(CASE WHEN (tag = 'fuzz') THEN 1 ELSE null END) has_fuzz
FROM nv_tags
GROUP BY entrieid
HAVING has_rousseau != 0 and has_fuzz != 0
) tags ON (entries.id = tags.entrieid)
JOIN nv_images images ON (tags.entrieid = images.entrieid);

Answer 2

SELECT * FROM
nv_entries entries
INNER JOIN nv_tags tags ON tags.entrieid = entries.id
INNER JOIN nv_images imgs ON imgs.entrieid = entries.id
WHERE tags.tag IN('rousseau','fuzz')
but this will extract all data from three tables.
specify your tags relative to the table to avoid redundant tags as entrieid.