MYSQL multiple grouping with join - php

Question

SELECT
p.product,
q.format,
p.title
FROM
product p
JOIN info q ON p.product = q.product
WHERE p.user='$user'
GROUP BY p.product,q.format
I want to first group by 'product' from the product table but the also by format on the info table.
This is to not show duplicates of format and product. At the moment only the grouping by product is working.
Table - products
product | title
0 one
1 two
1 two - a
2 three
Table - product_details
product | title | format |
0 one home
1 two home
1 two - a home
2 three work
So for this example I want a list like:
product | title | format
0 one home
2 three work
Instead of:
product | title | format
0 one home
1 two home
2 three work

Answer 1

After your table structures were posted, I can see what your intent is, I believe. It looks like you are attempting to limit your output result set to those values for product.product which are never repeated. That is, values for product.product which have exactly one product.title.
For that, you can use a GROUP BY aggregation to return only those with COUNT(*) = 1 after the group is applied.
In this case, since you only expect one row back per product.product anyway, you can do the aggregation at the top level, not requiring a subquery. If you had joined in other tables, and ended up getting multiple rows back per product due to other one-to-many relationships, you would need to use the subquery method instead (to be portable anyway - MySQL would still probably allow this)
SELECT
p.product,
q.format,
p.title
FROM
products p
JOIN product_details q ON p.product = q.product
GROUP BY
p.product,
q.format,
p.title
HAVING COUNT(*) = 1
Here is a demonstration: http://sqlfiddle.com/#!2/72eda/6
If you did expect multiple rows back per p.product, such as if you joined in additional one-to-many related tables, an efficient way to handle that is to perform a JOIN against a subquery that imposes that limit in the HAVING clause. Those which don't meet the HAVING condition won't be returned in the subquery and therefore get discarded by the INNER JOIN.
SELECT
p.product,
q.format,
p.title
FROM
products p
INNER JOIN product_details q ON p.product = q.product
/* Subquery returns only product values having exactly 1 row */
INNER JOIN (
SELECT product
FROM products
GROUP BY product
HAVING COUNT(*) = 1
) pcount ON p.product = pcount.product
WHERE p.user = '$user'
http://sqlfiddle.com/#!2/72eda/2