Re: GROUP BY

Ron Piggott wrote:

I run a once daily e-mail list. The users are able to choose the time of day they receive their daily e-mail. Their preference is stored in the email-delivery_hour field. I am trying to determine which email_delivery_hour between 0 and 6 has the lowest number of subscribers. (I am trying to make it so the same number of e-mails are sent out every hour by offering this as the default when people sign up.) The GROUP BY section on mySQL's web site didn't make sense to me. I have attempted to start making the query (below). What additional changes to do I need to make?

group by is for aggregation. eg you want to know the number of articles per category: select category_id, count(article_id) from articles group by category_id; so you have to use an aggregate function (count, sum, avg) and group by your unit field. In your case you want to get the number of subscribers (what you want to aggregate on) per email_delivery_hour (your unit field) which translates to: select count(member_id), <-- guessed the fieldname. Adjust it email_delivery_hour from member_subscriptions where list=1 and email_delivery_hour <= 6 group by email_delivery_hour order by email_delivery_hour ; -- Postgresql & php tutorials http://www.designmagick.com/