MySQL SELECT query returns wrong result - mysql

Question

I have a table orders(c_id(INT),o_date(DATE),o_price(INT)). I have to find out the id and MAX value of total price for each id in the current year. The table is as follows:
c_id o_date o_price
1 2017-08-27 30
2 2017-05-25 100
2 2017-05-02 20
1 2017-02-23 80
3 2017-01-26 60
4 2016-04-22 10
2 2016-03-15 5
1 2015-09-01 1
I code as follow:
SELECT c_id, MAX(m_price)
FROM ( SELECT c_id, SUM(o_price) AS
m_price FROM orders WHERE
( YEAR(o_date) = YEAR(curdate()) )
GROUP
> BY c_id )AS T
the MAX value return right but the id is not fit with that MAX value. Has anyone a suggestion for my situation? Thank you in advance!!

Answer 1

If there is guaranteed to be only one c_id which has the largest sum, or you don't mind returning only one result in the event of a tie, then you can just LIMIT 1 along with an ORDER BY to get the max result.
SELECT
c_id,
SUM(o_price) AS m_price
FROM orders
WHERE
YEAR(o_date) = YEAR(CURDATE())
GROUP BY c_id
ORDER BY m_price DESC
LIMIT 1
If there could be a tie for maximum sum, then there are workarounds which are slightly uglier, e.g.
SELECT
c_id,
SUM(o_price) AS m_price
FROM orders
WHERE
YEAR(o_date) = YEAR(CURDATE()) AND
GROUP BY c_id
HAVING SUM(o_price) =
(
SELECT MAX(t.m_price)
FROM
(SELECT SUM(o_price) AS m_price FROM orders
WHERE YEAR(o_date) = YEAR(CURDATE()) GROUP BY c_id) t
)
The above query is a bit verbose, and in other databases we would use analytic functions to handle this. But since MySQL does not support these out of the box we need to use another way.

Answer 2

If you have multiple prices, the following is slightly simpler than Tim's code:
SELECT o.c_id, SUM(o.o_price) AS m_price
FROM orders o
WHERE YEAR(o.o_date) = YEAR(CURDATE())
GROUP BY o.c_id
HAVING m_price = (SELECT SUM(o2.o_price)
FROM orders o2
WHERE YEAR(o2.o_date) = YEAR(CURDATE()
GROUP BY c_id
ORDER BY SUM(o2.o_price) DESC
LIMIT 1
);
In practice, using variables might be faster.
SELECT o.*
FROM (SELECT o.*, #maxp := GREATEST(#maxp, m_price)
FROM (SELECT o.c_id, SUM(o.o_price) AS m_price
FROM orders o
WHERE YEAR(o.o_date) = YEAR(CURDATE())
GROUP BY o.c_id
) o CROSS JOIN
(SELECT #maxp := 0) params
) o
WHERE m_price = #maxp;

Answer 3

Adjust your query as
SELECT c_id, MAX(m_price)
FROM ( SELECT c_id, SUM(o_price) AS
m_price FROM orders WHERE
YEAR(o_date) = YEAR(curdate())
)
GROUP BY c_id

Answer 4

My solution for this is:
set #p1 = (SELECT MAX(m_price) FROM
(
SELECT c_id, SUM(o_price) AS m_price FROM orders WHERE
(
YEAR(o_date) = YEAR(curdate())
) GROUP BY c_id
) as T
);
SELECT c_id from (
SELECT c_id, sum(o_price) as m_price from orders WHERE (
YEAR(o_date) = YEAR(curdate())
)group by c_id
) as a WHERE m_price = #p1