MYSQL从3个具有ID数组的表中选择结果

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()