Question

I am creating an online store website that needs the functionality to select a random product from the database.

The idea is that there will be an advert for a random product that is different each time the webpage loads!

Using PHP, how would I go about doing this?

tbl_products

id
code
title
stock
cost
rrp

These are the rows I need to get access to from the database.

Thanks

Answer 1

A most straightforward solution would be this:

SELECT  *
FROM    tbl_products
ORDER BY
        RAND()
LIMIT 1

However, this becomes less efficient as the number of products grows.

This solution:

• Selecting random rows

is more efficient, though it still requires a full table scan.

If you product ids are distributes more or less uniformly, use this:

SELECT  p.*
FROM    (
        SELECT
                (
                (
                SELECT  MAX(id)
                FROM    tbl_products
                ) -
                (
                SELECT  MIN(id)
                FROM    tbl_products
                )
                ) * RAND() AS rnd
        ) q
JOIN    tbl_products p
ON      id >= rnd
ORDER BY
        id
LIMIT 1;

If you have gaps between ids, the products after large gaps will tend to be selected more often.

Instead of id, you may use a special unique column for this purpose which you should fill without gaps in a cron job.