Mysql search on multiple join results - mysql

Question

I've a table "products" and a table where are store some attributes of a product:
zd_products
----------
|ID|title|
----------
| 1| Test|
| 2| Prod|
| 3| Colr|
zd_product_attached_attributes
------------------
|attrid|pid|value|
------------------
|1 | 1 | A |
|2 | 1 | 10 |
|3 | 1 | AB |
|1 | 2 | B |
|2 | 2 | 22 |
|3 | 2 | BB |
|1 | 3 | A |
|2 | 3 | 10 |
|3 | 3 | CC |
I want to search in zd_products only the products that have some attributes values, for exam place
Get the product when the attribute 1 is A and the attribute 3 is AB
Get the product when the attribute 2 is 10 and the attribute 3 is CC
etc
How can i do this using a join ?

Answer 1

Oh, the Joys of the EAV model!
One way is to use a separate JOIN operation for each attribute value. For example:
SELECT p.id
, p.title
FROM zd_products p
JOIN zd_product_attached_attributes a1
ON a1.pid = p.id
AND a1.attrid = 1
AND a1.value = 'A'
JOIN zd_product_attached_attributes a3
ON a3.pid = p.id
AND a3.attrid = 3
AND a3.value = 'AB'
With appropriate indexes, that's likely going to be the most efficient approach. This isn't the only query that will return the specified result, but this one does make use of JOIN operations.
Another, less intuitive approach
If id is unique in the zd_products table, and we have guarantee that the (attrid,pid,value) tuple is unique in the zd_product_attached_attributes table, then this:
SELECT p.id
, p.title
FROM zd_products p
JOIN zd_product_attached_attributes a
ON a.pid = p.id
AND ( (a.attrid = 1 AND a.value = 'A')
OR (a.attrid = 3 AND a.value = 'AB')
)
GROUP
BY p.id
, p.title
HAVING COUNT(1) > 1
will return an equivalent result. The latter query is of a form that is particularly suitable for matching two criteria out of three, where we don't need a match on ALL of the attributes, but just some of them. For example, finding a product that matches any two of:
color = 'yellow'
size = 'bigger'
special = 'on fire'
And of course there are other approaches that don't make use of a JOIN.
FOLLOWUP
Q: And if I want to the same but using OR operator? I mean get ONLY if the attribute 1 is A or the attribute 2 is AB otherwise don't select the record.
A: A query of the form like the second one in my answer (above) is more conducive to the OR condition.
If you want XOR (exclusive OR), where one of the attributes has a matching value but the other one doesn't, just change the HAVING COUNT(1) > 1 to HAVING COUNT(1) = 1. Only rows from products that find one "matching" row in the attributes table will be returned. To match exactly 2 (out of several), HAVING COUNT(1) = 2, etc.
A query like the first one in my answer can be modified to use OUTER joins, to find matches, and then do a conditional test in the WHERE clause, to determine if a match was found.
SELECT p.id
, p.title
FROM zd_products p
LEFT
JOIN zd_product_attached_attributes a1
ON a1.pid = p.id
AND a1.attrid = 1
AND a1.value = 'A'
LEFT
JOIN zd_product_attached_attributes a3
ON a3.pid = p.id
AND a3.attrid = 3
AND a3.value = 'AB'
WHERE a1.pid IS NOT NULL
OR a3.pid IS NOT NULL
I've just added the LEFT keyword, to specify an outer join; rows from products will be returned with matching rows from a1 and a3, along with rows from products that don't have any matching rows found in a1 or a3.
The WHERE clause tests a column from a1 and a3 to see whether a matching row was returned. If a matching row was found in a1, we are guaranteed that the pid column from a1 will be non-NULL. That column will be returned as NULL only if a matching row was not found.
If we replaced the OR with an AND, we'd be negating the "outerness" of both joins, making it essentially equivalent to the first query above.
To get an XOR type operation (exclusive OR) where we find one matching attribute but not the other, we could change the WHERE clause to read:
WHERE (a1.pid IS NOT NULL AND a3.pid IS NULL)
OR (a3.pid IS NOT NULL AND a1.pid IS NULL)

Answer 2

Use a pivot
You can do this type of query using a pivot. As far as I know, MySQL doesn't have a native, built in pivot, but you can achieve this by transposing the rows and columns of your zd_product_attached_attributes table using:
SELECT pid,
MAX(CASE WHEN attrid = 1 THEN value END) `attrid_1`,
MAX(CASE WHEN attrid = 2 THEN value END) `attrid_2`,
MAX(CASE WHEN attrid = 3 THEN value END) `attrid_3`
FROM zd_product_attached_attributes
GROUP BY pid
This will pivot your table as shown:
+----+---------+-------+ +----+----------+----------+----------+
| attrid | pid | value | | pid| attrid_1 | attrid_2 | attrid_3 |
+----+---+-------------+ +----+----------+----------+----------+
| 1 | 1 | A | | 1 | A | 10 | AB |
| 2 | 1 | 10 | => | 2 | B | 22 | BB |
| 3 | 1 | AB | | 3 | A | 10 | CC |
| 1 | 2 | B | +----+----------+----------+----------+
| 2 | 2 | 22 |
| 3 | 2 | BB |
| 1 | 3 | A |
| 2 | 3 | 10 |
| 3 | 3 | CC |
+--------+---------+---+
So you can select the products id and title using:
SELECT id, title FROM zd_products
LEFT JOIN
(
SELECT pid,
MAX(CASE WHEN attrid = 1 THEN value END) `attrid_1`,
MAX(CASE WHEN attrid = 2 THEN value END) `attrid_2`,
MAX(CASE WHEN attrid = 3 THEN value END) `attrid_3`
FROM zd_product_attached_attributes
GROUP BY pid
) AS attrib_search
ON id = pid
WHERE ( attrib_1 = 'A' AND attrib_3 = 'AB' )
OR ( attrib_2 = 10 AND attrib_3 = 'CC' )
Note: You can use this type of query when you have guaranteed uniqueness on (pid, attrid)
(thanks #spencer7593)

Answer 3

I haven't tested this, but I think it should work:
select title
from zd_products p
join zd_product_attached_attributes a ON a.pid = p.id
where ( attrid = 1 and value = 'A' )
or ( attrid = 3 and value = 'AB' );
If you want to tack on more "searches" you could append more lines similar to the last one (ie. or "or" statements)