Question

I have 2 tables, named subscriptions and tags. Once in a month I will have to create tags for each order.

I have to list subscriptions without a tag for the given month (2011-10-01 or 2011-09-01 etc). This query returns 0 records:

   SELECT s.id, s.active, s.status 
     FROM asw_subscriptions as s 
LEFT JOIN asw_tags as t ON s.id = t.subscription_id 
    WHERE t.subscription_id IS NULL 
      AND t.deliveryDate = '2011-10-01' 
      AND s.status = '2' 
      AND s.active = '1' 
 ORDER BY s.id DESC 
    LIMIT 0, 25

Table Structure

---

subscriptions = id (int / auto), active (enum : 0,1), status (enum : 0,1)

tags = id (int / auto), deliveryDate (date), tagNumber

Answer 1

The problem is in clausule

t.deliveryDate = '2011-10-01' AND

You have not record on the left because condition ‘IS NULL’ eliminates LEFT JOIN’ed records.
So, above condition will eliminate all join products, because will never be true (there will be always null in t.deliveryDate.

Try something like this:

SELECT s.id, s.active, s.status 
     FROM asw_subscriptions as s 
WHERE s.status = '2' 
      AND s.active = '1' 
      AND NOT EXISTS (
         SELECT 1
         FROM asw_tags as t
         WHERE s.id = t.subscription_id
         AND t.deliveryDate = '2011-10-01'          
      )
 ORDER BY s.id DESC 
    LIMIT 0, 25