I have this Query :
SELECT sl.sms_prefix, sum( sl.parts ) , cp.country_name, CAST(SUM(sl.parts) AS NUMERIC(10,4)) * CAST(cp.price AS NUMERIC(10,4))
FROM sms_log sl, sms_transaction st, country_prefix cp
WHERE st.customer_id =1
AND st.sendtime >=1329865200
AND st.sendtime <=1330037999
AND st.sms_trans_id = sl.trans_id
AND sl.sms_prefix = cp.prefix
AND st.customer_id = cp.customer_id
GROUP BY sl.sms_prefix
LIMIT 0 , 30Result:
sms_prefix sum( sl.parts ) country_name price total
==================================================================================
45 2 Denmark 0.01 0.019999999552965
63 3 Philippines 2 6As you see the "total" is not correct for Denmark because sum( sl.parts )=2 Multiply with 0.01 the total should be 0.02.
Price field is FLOAT how I can CAST the total to float ?
Regards,
02 Answers
While @Heximal's answer works, I don't personally recommend it.
This is because it uses implicit casting. Although you didn't type CAST, either the SUM() or the 0.0 need to be cast to be the same data-types, before the + can happen. In this case the order of precedence is in your favour, and you get a float on both sides, and a float as a result of the +. But SUM(aFloatField) + 0 does not yield an INT, because the 0 is being implicitly cast to a FLOAT.
I find that in most programming cases, it is much preferable to be explicit. Don't leave things to chance, confusion, or interpretation.
If you want to be explicit, I would use the following.
CAST(SUM(sl.parts) AS FLOAT) * cp.price
-- using MySQL CAST FLOAT requires 8.0I won't discuss whether NUMERIC or FLOAT *(fixed point, instead of floating point)* is more appropriate, when it comes to rounding errors, etc. I'll just let you google that if you need to, but FLOAT is so massively misused that there is a lot to read about the subject already out there.
You can try the following to see what happens...
CAST(SUM(sl.parts) AS NUMERIC(10,4)) * CAST(cp.price AS NUMERIC(10,4))In oracle db there is a trick for casting int to float (I suppose, it should also work in mysql):
select myintfield + 0.0 as myfloatfield from mytable
