Question

I’m writing a simple URL rotator for a client and they want the URLs to rotate according to the oldest one that was previously displayed.

My columns are very simple:

url_id | company_id | url | last_clicked

I want to fetch a single row where the company_id is passed in and the last_clicked is the minimum of all records matching the company_id.

It should also select a random url_id if all last_clicked values are empty.

I assume this can be accomplished with a GROUP BY and HAVING but I can’t seem to get the query to return anything.

I have this:

$last = $this->db->fetchOne ("SELECT url_id FROM 
        {$this->prefix}urls GROUP BY company_id HAVING MIN(last_clicked) 
        WHERE company_id='$company'");

Answer 1

This will fetch the row where last_clicked is smallest, or at random if they are all NULL:

SELECT url_id FROM urls 
    WHERE company_id = $company
    ORDER BY last_clicked, RANDOM() LIMIT 1;

An index based on company_id and last_clicked would greatly help:

CREATE INDEX urls_ndx ON urls(company_id, last_clicked);