Question

Goal:

Need results for channels that are active (channels.active=1) but have 0 active items.

There are items and they belong in channel. items can have multiple channels.

There are 3 tables:

• channels
• items
• items_channels

The items_channel maps items to channels. Example row:

id  item   channel
1   23     47 

So far I just have this to get active channels:

SELECT * FROM channels WHERE channels.active = 1

I’m having trouble grasping the part where I only join the channels that have 0 active items – do I need a subquery or a HAVING clause that has a COUNT somewhere?

Also, channels.active is for active channels, and items.active is for active items.

Answer 1

This should work for you:

SELECT channels.* 
FROM channels
LEFT JOIN items_channels
  ON channels.id = items_channels.channel
LEFT JOIN items
  ON items_channels.item = items.id AND items.active = 1
WHERE channels.active = 1
GROUP BY channels.id
HAVING COUNT(items.id) = 0

Working sqlfiddle here.