Self-referencing SQL statement - mysql

Question

Overview: I need to write an custom SQL question in ExpressionEngine.
I have a product table (exp_channel_titles) that is assigned categories (exp_category_posts). In EE categories are grouped (as defined in exp_categories).
Here's what I'm trying to do...
When I'm displaying a particular product (single row), I want to go back to the product table and pull random "suggestions" as based on the categories in a certain category group of the displayed product. Finally, I want to be sure to exclude the displayed product from the suggestions.
My SQL is ok but this is fairly advance in my book. I'm here hoping to get some helps.
Thus far I can get the single row and it's categories from the category group I'm interested in. But now what?
SELECT *
FROM exp_channel_titles
LEFT JOIN exp_category_posts
ON exp_channel_titles.entry_id = exp_category_posts.entry_id
LEFT JOIN exp_categories
ON exp_category_posts.cat_id = exp_categories.cat_id
WHERE exp_channel_titles.entry_id = "17" AND exp_categories.group_id = "3"
Thanks in advance for your help.
-- UPDATE --
I suppose this is brute force but it works, almost.
SELECT *
FROM exp_channel_titles my1
LEFT JOIN exp_category_posts my2
ON my1.entry_id = my2.entry_id
LEFT JOIN exp_category_posts my3
ON my1.entry_id = my3.entry_id
LEFT JOIN exp_category_posts my4
ON my1.entry_id = my4.entry_id
WHERE my3.cat_id = "7" AND my2.cat_id = "2" AND my1.entry_id != "17" AND my4.cat_id IN (
SELECT exp_category_posts.cat_id
FROM exp_category_posts
LEFT JOIN exp_categories ON exp_category_posts.cat_id = exp_categories.cat_id
WHERE exp_category_posts.entry_id = '17' AND exp_categories.group_id = '3'
)
Since I'm needing to filter by categories from 3 different category groups I do 3 LEFT JOINs. The first two are just focused on a single category (2=published, 7=music), the third could return multiple values from the subquery so I'm using IN. The subquest asked For entry_id = X (in this case 17, which is the main/single product being displayed) what categories from group_id=3 (music) should I be suggesting?
The final question is, since the subquery returned multiple rows, the main select can return dupes. I want a list of unique products. What now? Group by? Order by?
Pardon this nooby question but to be honest Google sucks when it comes to finding answers. There's tons of crap examples, unanswered questions, etc. I'm know the concepts, but my syntax is rusty. Please help a brother out.
If anyone see any easy way to optimize the above, I'll glad listen. Thank you again.

Answer 1

You can do this with native EE tags using related categories mode. Just make a new channel:entries loop outside of your main product channel:entries tag, or embed it if you have to.

Answer 2

I'd suggest embedding a template within your channel:entries loop, and passing the current entry_id as an embed parameter.
{embed="embeds/related_products" entry_id="{entry_id}"}
Then in your embedded template:
{exp:channel:entries channel="products" category_group="3|4" entry_id="not {embed:entry_id}" limit="5" orderby="random"}
// variables here
{/exp:channel:entries}

Answer 3

DISCLAIMER: Not sure if this will work, and it could very likely do with some optimization, but perhaps this will work:
SELECT DISTINCT ect.*
FROM
exp_channel_titles ect
LEFT JOIN exp_category_posts ecp ON ect.entry_id = ecp.entry_id
LEFT JOIN exp_categories ec ON ecp.cat_id = ec.cat_id
WHERE
ect.entry_id != '17'
AND ec.group_id IN (
SELECT ec.group_id
FROM
exp_channel_titles ect
LEFT JOIN exp_category_posts ecp ON ect.entry_id = ecp.entry_id
LEFT JOIN exp_categories ec ON ecp.cat_id = ec.cat_id
WHERE
ect.entry_id = '17'
);