Question

I have 2 tables:

money_change:

id_change | id_factor | d_change | date
--------------------------------------------- 
1           5           0.10       2012-06-07
2           6           0.11       2012-06-07
3           5           0.12       2012-06-09
4           6           0.11       2012-06-10
5           8           1.09       2012-06-03  

money_factor:

id_factor | money_base | money_change
--------------------------------------
5           'Dollar'     'Yen' 
6           'Dollar'     'Euro'
7           'Euro'       'Dollar'
8           'Euro'       'Yen'

I’m trying to do a query that returns me the latest changes in currency to the dollar. I mean the result:

id_factor | d_change | date
--------------------------------------
5           0.12       2012-06-09
6           0.11       2012-06-10

I can know the last date for individual factor:

SELECT MAX( date )
FROM money_change
WHERE id_factor = 6

but as you might know the last date for each factor of “Dollar”? I tried something like this:

SELECT id_factor, d_change, date
FROM money_change c
INNER JOIN money_factor f
ON f.id_factor = c.id_factor
LEFT JOIN (
    SELECT MAX(date) AS date
    FROM money_change
) AS Last
ON c.dRegistro = Last.date
WHERE money_base = "Dollar"

but I returned:

id_factor | d_change | date
--------------------------------------
5           0.10       2012-06-07
6           0.11       2012-06-07
5           0.12       2012-06-09
6           0.11       2012-06-10

I think I need to enter the ‘where’ in the subquery, but as it dynamically for each factor?

Answer 1

Try this query:

SELECT
    t.id_factor,
    t.d_change,
    t.date
FROM
(
    SELECT
         mc.id_factor,
         mc.d_change,
         mc.date
    FROM
        money_change mc
    INNER JOIN
        money_factor mf USING(id_factor)
    WHERE
        mf.money_base = "Dollar"
    ORDER BY
        mc.date DESC
) t
GROUP BY
    t.id_factor