Question

I have a table called ORDEREXECUTIONS that stores all orders that have been executed. It’s a multi currency application hence the table has two columns CURRENCY1_ID and CURRENCY2_ID.

To get a list of all orders for a specific currency pair (e.g. EUR/USD) I need to lines to get the totals:

v = Orderexecution.where("is_master=1 and currency1_id=? and currency2_id=? and created_at>=?",c1,c2,Time.now()-24.hours).sum("quantity").to_d
v+= Orderexecution.where("is_master=1 and currency1_id=? and currency2_id=? and created_at>=?",c2,c1,Time.now()-24.hours).sum("unitprice*quantity").to_d

Note that my SUM() formula is different depending on the the sequence of the currencies.
e.g. If I want the total ordered quantities of the currency pair USD it then executes (assuming currency ID for USD is 1 and EUR is 2.

v = Orderexecution.where("is_master=1 and currency1_id=? and currency2_id=? and created_at>=?",1,2,Time.now()-24.hours).sum("quantity").to_d
v+= Orderexecution.where("is_master=1 and currency1_id=? and currency2_id=? and created_at>=?",2,1,Time.now()-24.hours).sum("unitprice*quantity").to_d

How do I write this in RoR so that it triggers only one single SQL statement to MySQL?

Answer 1

I guess this would do:

v = Orderexecution.where("is_master=1 
                           and ( (currency1_id, currency2_id) = (?,?)
                              or (currency1_id, currency2_id) = (?,?)
                               )
                           and created_at>=?"
                        ,c1, c2, c2, c1, Time.now()-24.hours
                        )
                  .sum("CASE WHEN currency1_id=? 
                               THEN quantity 
                             ELSE unitprice*quantity 
                        END"
                      ,c1 
                      )
                  .to_d