Question

I have 3 tables that look like this:

• Table 1 (main table):

  item_id (item_id, item_name) // item_id set to primary 
  row1    (1,       "item 1")
  row2    (2,       "item 2")
  row3    (3,       "item 3")
  

• Table 2 (linking table):

  item_keywords (ikid, #item_id, #keyword_id) // ikid is set to primary 
  row1          (1,       1,     1)
  row2          (2,       1,     2)
  row3          (3,       1,     3)
  row4          (4,       2,     1)
  row5          (5,       3,     1) 
  

• Table 3:

  keywords (keyword_id, keyword_name) // keyword_id is set to primary 
  row1          (1,       "key1")
  row2          (2,       "key2")
  row3          (3,       "key3")
  row4          (4,       "key4")
  row5          (5,       "key5") 
  

I would like to make a query that returns all items that contain certain keywords AND also don’t contain some other keywords.

If you look at the table data above you can see that:

Item 1 contains keywords with ids: 1,2 and 3; 
Item 2 contains keyword with id: 1 
item 3 contains keyword_id =1 

So I need a query that will return all items that contain key1 (keyword_id=1) and DON’T contain key3 (keyword_id=3). In this exmaple the query should return key2 (keyword_id=2), key3 (keyword_id=3).

Something like this:

SELECT a.*
FROM items a
JOIN item_keywords b ON b.item_id = a.item_id
WHERE b.keyword_id = 1
   AND b.keyword_id != 3

But this doesn’t work properly because the query returns key1,key2 and key3. The answer should be: key2 and key3. What would be the simplest way of doing this?

Answer 1

SELECT i.*
FROM items AS i
INNER JOIN item_keywords AS ik ON i.item_id = ik.item_id
WHERE keyword_id = 1
   AND ik.item_id NOT IN
   (
      SELECT item_id
      FROM item_keywords
      WHERE keyword_id = 3
   )

Example of query working: