Use most recent date for missing dates when joining tables

Question

I have 2 tables:

1.tran_test : (id, amount, currency(Currency_Name), date_1)
2.cur_test: (id, currency, date_2, price(amount In USD))

How t

Answer 1

select date_1, SUM(amount*c.price) AS sum_by_day
from
(
    select *, max (date_2) as lastDate
    from tran_test AS t
    INNER JOIN cur_test AS c
    ON t.currency = c.currency AND date_1 >= date_2
    GROUP BY date_1;
) as t
INNER JOIN cur_test AS c
ON t.currency = c.currency AND lastdate = date_2
GROUP BY date_1;

Answer 2

Write a subquery that finds the most recent date in the currency table for each date in the transaction table.

SELECT t.date_1, MAX(c.date_2) AS latest_date
FROM tran_test AS t
JOIN cur_test AS c ON t.date_1 >= c.date_2
GROUP BY t.date1

You can then join this with the rest of your query.

SELECT t.date_1, SUM(t.amount * c.price) AS sum_by_day
FROM tran_test AS t
JOIN (
    SELECT t.date_1, MAX(c.date_2) AS latest_date
    FROM tran_test AS t
    JOIN cur_test AS c ON t.date_1 >= c.date_2
    GROUP BY t.date1) AS g ON g.date_1 = t.date_1
JOIN cur_test AS c ON c.date_2 = g.latest_date
GROUP BY t.date_1