MYSQL join on condition1 else join on condition2 - php

Question

I've got two tables where I want to JOIN one with the other. The JOIN works fine, but I get two records returned. This is (looking at my query) correct, but I need to return one of the two records based on a condition. Can this be managed with a single query?
table oc_order_product:
product_id | name | quantity | order_id | store_url
51 | prod1 | 1 | 17 | http://www.opencarttest.com/
48 | prod2 | 3 | 17 | http://www.opencarttest.com/
table product:
oc_product_id | price | store_url
51 | 50.00 | http://www.opencarttest.com/
51 | 89.95 |
48 | 15.00 |
My current query:
SELECT
oop.product_id,
oop.name,
oop.quantity,
p.price,
p.store_url
FROM
oc_order_product AS oop
JOIN
product AS p
ON
p.oc_product_id = oop.product_id
WHERE
oop.order_id='17' AND oop.store_url='http://www.opencarttest.com/'
This returns:
product_id | name | price | store_url
51 | prod1 | 50.00 | http://www.opencarttest.com/
51 | prod1 | 89.95 |
48 | prod2 | 15.00 |
But I need only this:
product_id | name | price | store_url
51 | prod1 | 50.00 | http://www.opencarttest.com/
48 | prod2 | 15.00 |
I only need one result from product that matched the oc_product_id. But it can be one of both products. I need the product with the store_url equals the oc_order_product.store_url, or else the product without the store_url.
EDIT: Added trailing slashes

Answer 1

This will give you what you are looking for, however at the expense of performance:
SELECT
oop.product_id,
oop.name,
oop.quantity,
p.price,
p.store_url
FROM
oc_order_product AS oop
JOIN
product AS p
ON
p.oc_product_id = oop.product_id
and
(p.store_url = oop.store_url
or
not exists (select 1 from product where oc_product_id=p.oc_product_id and store_url is not null)
)
WHERE
oop.order_id='17' AND oop.store_url='http://www.opencarttest.com'
Here is the sqlfiddle.
Note that with your specific data as shown in the question, this won't work - and neither will your own query - as you have URL's with the trailing slash in one table and without it in the other. In my example, I removed trailing slashes in all places.

Answer 2

Updated - I made an assumption that fields were empty strings instead of NULLs
Thanks to #aleks-g since I stole his SQLFiddle for this code test
Here is one way - Using LEFT JOINs and COALESCES
SELECT
oop.product_id,
oop.name,
oop.quantity,
COALESCE(p_filled.price, p.price) AS price,
COALESCE(p_filled.store_url, p.store_url) AS store_url
FROM oc_order_product AS oop
LEFT JOIN product AS p_filled
ON p_filled.oc_product_id = oop.product_id
AND oop.store_url= p_filled.store_url
LEFT JOIN product AS p
ON p.oc_product_id = oop.product_id
AND COALESCE(p_filled.store_url,'') = ''
WHERE
oop.order_id='17' AND oop.store_url='http://www.opencarttest.com';

Answer 3

You can use the mysql variable in your query to record the occurrence of product id and by using CASE you can check either product has url OR product is not repeated then select it,some columns in query are just to elaborate the working
SELECT
oop.product_id,
oop.name,
oop.quantity,
p.price,
p.store_url,
(CASE when #test=oop.product_id then 'repeated'
else 'new' end) occurance,
(CASE when p.store_url =oop.store_url OR #test!=oop.product_id
then 'has'
else 'none' end) url,
#test:=oop.product_id `testvar`
FROM
oc_order_product AS oop
join (SELECT #test:=0) t
JOIN
(SELECT * FROM product ORDER BY store_url DESC) AS p
ON
p.oc_product_id = oop.product_id
WHERE
oop.order_id='17'
HAVING url='has'
Fiddle Demo

Answer 4

$rs = $db->Select('products p, products_images pi','p.*,image_id',"p.product_id=pi.product_id","product_id=$a1");

Answer 5

Here's another way to do it, without requiring a subquery:
SELECT
oop.product_id,
oop.name,
oop.quantity,
IFNULL(p1.price, p2.price),
p1.store_url
FROM
oc_order_product AS oop
LEFT JOIN
product AS p1
ON
p1.oc_product_id = oop.product_id AND p1.store_url = oop.store_url
LEFT JOIN
product AS p2
ON
p2.oc_product_id = oop.product_id
WHERE
oop.order_id='17'
AND oop.store_url='http://www.opencarttest.com/'
AND p1.oc_product_id IS NOT NULL OR p2.oc_product_id IS NOT NULL