Question

Hello guys I have a problem with a query and left join

I have 2 tables products and characteristics
I know some required characteristics with id 1,3,6

 SELECT * FROM products
    LEFT JOIN characteristics ...
    WHERE characteristics_id IN (1,2,6)

But this not works for me because I need the products with ALL of this characteristics, not only one.

Really I need

 SELECT * FROM products
    INNER JOIN characteristics as c1 ... AND c1.id=1
    INNER JOIN characteristics as c2 ... AND c2.id=2
    INNER JOIN characteristics as c2 ... AND c2.id=3
...

But it don’t like me, there must be a simpler and efficient

Thank you.

Answer 1

First of all, you don’t need a LEFT JOIN at all.

Second, your first attempt seems perfectly valid and I think it’s the most efficient (when there are indexes on the tables to be joined). But I’m adding another way (that seems more simple as it has only 1 join).

---

Simple (to add more than 3 characteristics):

SELECT p.*
FROM products AS p
  INNER JOIN characteristics AS c ON ...
WHERE c.id IN (1, 3, 6)
GROUP BY p.id
HAVING
  COUNT(*) = 3             --- or COUNT(DISTINCT c.id)
                           --- depending on your data

---

More efficient (in most cases, in other words: test, test and test again in your tables with various sizes and number of ids):

SELECT p.* 
FROM products AS p
  INNER JOIN characteristics AS c1 ON ... 
  INNER JOIN characteristics AS c2 ON ... 
  INNER JOIN characteristics AS c3 ON ... 
WHERE c1.id = 1 
  AND c2.id = 3 
  AND c3.id = 6