How to chain or combine scopes with subqueries or find_by_sql

问题

I would like to perform a query like

SELECT * FROM ( SELECT * FROM products ORDER BY price ASC ) AS s GROUP BY item;

which return the cheapest of all products for each item. Using this subquery is good because it can run in O(N logN) time.

So I can find this with find_by_sql, but it would be nice to be able to chain it with other scopes for Product.

Anyone know how to either write this as a scope or chain scoped and find_by_sql?

回答1:

You should be able to do something like

Product.from("(SELECT * FROM products ORDER BY price ASC) AS products").group(:item)

来源：https://stackoverflow.com/questions/4878856/how-to-chain-or-combine-scopes-with-subqueries-or-find-by-sql