MYSQL select results from 3 tables with an array of ids - mysql

Question

Ok, so I have 3 mysql tables where I need to extract data from. Anything to do with joins really gets me stuck!
Table 1 = products (productid, name)
Table 2 = category (categoryid, name)
Table 3 = categoryproduct (categoryid, productid) - my join table
I have an array of product ids which I need to get a random selection of products that fall into the same categories as these products.
The idea is that the results of the query will display a section in my cart of similar/related products that the customer may like
So something like
SELECT name etc FROM table1
WHERE table2.categoryid of results of the query = table3.categoryid of current products
ORDER BY RAND()
LIMIT 3
How do I write that??

Answer 1

Assuming you're using PHP, following method will fetch 10 related products from database.
$productids = array(1002,789,999,203,321);
$sql = '
SELECT * FROM
products p JOIN categoryproduct pc
ON p.productid = pc.productid
WHERE pc.categoryid IN(
SELECT DISTINCT(categoryid) FROM
products inner_p JOIN categoryproduct inner_pc
ON inner_p.productid = inner_pc.productid
WHERE inner_p.productid IN('.implode(',',$productids).')
)
ORDER BY RAND()
LIMIT 10';

Answer 2

If i have understood your problem correctly then this query may help. Here instead of subquery you can give comma separated string which contains categoryid of different products selected by the user.
select p.name
from products p,categoryproduct cp
where p.productid=cp.productid
and cp.categorid in(
select categoryid
from cartitems)
order by RAND()