Is it possible to include a sub-query inside a select statement? - sql

Question

I have the following three tables:
dbo_CURRENCYRATES
+-------------+---------+---------------+
|CURRENCY_ID |BUY_RATE |DATE_EFFECTIVE |
+-------------+---------+---------------+
|GBP |1.5 |01/01/2000 |
|USD |2.5 |01/01/2000 |
|EUR |0.5 |01/01/2000 |
|GBP |1.7 |01/01/2017 |
|USD |2.7 |01/01/2017 |
|EUR |0.7 |01/01/2017 |
+-------------+---------+---------------+
dbo_DISCOUNTRATES
+-------------+--------------+
|DISCOUNT |DISCOUNT_RATE |
+-------------+--------------+
|50 |0.5 |
|25 |0.25 |
|35 |0.35 |
+-------------+--------------+
dbo_CUSTOMER
+-------+---------------+---------+----------+
|ID |NAME |CURRENCY | DISCOUNT |
+-------+---------------+---------+----------+
|1 |Widgets INC |USD |50 |
|2 |Widgets GMBH |EUR |35 |
|3 |Widgets PLC |GBP |25 |
+-------+---------------+---------+----------+
and a query
CurrentExchangeRate
+--------------------------------------------+
SELECT
a.CURRENCY_ID
,a.BUY_RATE
FROM dbo_CURRENCYRATES AS t
INNER JOIN
(
SELECT
CURRENCY_ID
,MAX(DATE_EFFECTIVE) AS MaxDate
FROM dbo_CURRENCYRATES
GROUP BY dbo_CURRENCYRATES.CURRENCY_ID
) AS tm
ON (a.CURRENCY_ID = b.CURRENCY_ID)
AND (a.DATE_EFFECTIVE = b.MaxDate);
I have a select query which selects data from dbo_CUSTOMER which includes currency and discount.
SELECT
dbo_CUSTOMER.ID
,dbo_CUSTOMER.NAME
,dbo_CUSTOMER.CURRENCY_ID AS [CURRENCY]
,BUY_RATE
,dbo_CUSTOMER.DISCOUNT
,DISCOUNT_RATE
FROM dbo_CUSTOMER
WHERE ID = '1';
Is is possible to include in this query, a sub-query which lets me get the BUY_RATE for the currency (from a separate query) and the the appropriate discount rate by querying another table?
I have a separate query to get the currency rate, as I need to have the latest value for the specific currency.
So, in pseudo code, can I do this:
SELECT
dbo_CUSTOMER.ID
,dbo_CUSTOMER.NAME
,dbo_CUSTOMER.CURRENCY_ID AS [CURRENCY]
,dbo_CUSTOMER.DISCOUNT
,(
SELECT BUY_RATE
FROM CurrentExchangeRate
WHERE CurrentExchangeRate.CURRENCY_ID = [CURRENCY]
) as BUY_RATE
,(
SELECT DISCOUNT_RATE
FROM dbo_DISCOUNTRATES
WHERE dbo_DISCOUNTRATES.DISCOUNT = dbo_CUSTOMER.DISCOUNT
) as DISCOUNT_RATE
FROM dbo_CUSTOMER
WHERE ID = '1';
Is is possible to do this, firstly in a query and secondly in an access database?
Thanks

Answer 1

Yes, you can. Only tip you need to know in your sub queries, for what you need, is that you need to select with a TOP 1, and ORDER BY DESC on the date field.