Question

I need help building a mysql query to select from multiple tables.
I have three database tables related to images: images, tags, tag_asc. I want to fetch an image data and its tag names by providing image_id.

For example, following is my tables structure:

images:

image_id    image_name     path       date   
1            test.jpg      dir       1311054433

tags:

tag_id      image_id
1             1
2             1

tag_asc:

tag_id      tag_name
1            "first"
2            "second"
3            "third"

I want to fetch the data of an image with image_id = 1 from images table and all tag names associated with image_id=1 from tag_asc table.

I’m using CodeIgniter Active records, but I just need idea of joining the tables.

Thanks for any help.

Answer 1

select *
from images i
left join tags t on t.image_id = i.image_id
left join tag_asc ta on ta.tag_id = t.tag_id
where i.image_id = 1;

Using LEFT JOIN means that rows will be returned even if there are no joining rows in the other tables (but you’ll get null values in the columns for the missing rows), which is typically desirable.

If you want one row (not stated in question, but in comments), use this:

select i.image_id, group_concat(tag_name) as tag_names
from images i
left join tags t on t.image_id = i.image_id
left join tag_asc ta on ta.tag_id = t.tag_id
where i.image_id = 1
group by 1;