MySQL: Find day with max orders - mysql

Question

I have a very basic orders table:
+----------+---------+------------+---------+
| order_id | cust_id | order_date | book_id |
+----------+---------+------------+---------+
| 1 | 1 | 10/10/2014 | 1 |
+----------+---------+------------+---------+
| 2 | 1 | 10/10/2014 | 2 |
+----------+---------+------------+---------+
| 3 | 1 | 10/12/2014 | 1 |
+----------+---------+------------+---------+
| 4 | 2 | 10/18/2014 | 6 |
+----------+---------+------------+---------+
| 5 | 2 | 10/18/2014 | 77 |
+----------+---------+------------+---------+
| 6 | 2 | 10/18/2014 | 103 |
+----------+---------+------------+---------+
| 7 | 2 | 10/10/2014 | 13 |
+----------+---------+------------+---------+
| 8 | 3 | 10/09/2014 | 1 |
+----------+---------+------------+---------+
| 9 | 3 | 10/11/2014 | 2 |
+----------+---------+------------+---------+
| 10 | 3 | 10/12/2014 | 3 |
+----------+---------+------------+---------+
The query should:
- For each customer show order_date with Max number of orders. Example: customer 1 had 2 orders on 10/10/2014
- Special case: When customer has multiple days with most orders, show the earliest date. Example: customer 3 had 3 single item orders on different days. Need to show 10/09/2014.
I should be able to solve this without use of temp tables.
Kira

Answer 1

You need two clauses: 1) find the max number of orders per customer per day and 2) find the day on which the max number of orders occurred. The second step is needed to eliminate multiple days with same number of orders.
SELECT * FROM
(SELECT cust_id,
order_date,
count() cnt
FROM
orders
GROUP BY cust_id, order_date) x
JOIN
(SELECT cust_id,
MAX(cnt) max_cnt
FROM
(SELECT cust_id,
order_date,
count() AS cnt
FROM
orders
GROUP BY cust_id, order_date) n
GROUP BY cust_id) y
ON
y.max_cnt = x.cnt
AND
y.cust_id = x.cust_id
JOIN (SELECT x.cust_id,
min(x.order_date) AS dd
FROM
(SELECT cust_id,
order_date,
count() cnt
FROM orders
GROUP BY by cust_id, order_date) x
JOIN
(SELECT cust_id,
MAX(cnt) max_cnt
FROM
(SELECT cust_id,
order_date,
count() as cnt
FROM
orders
GROUP BY
cust_id, order_date) n
GROUP BY cust_id) y
ON
y.max_cnt = x.cnt
AND
y.cust_id = x.cust_id
GROUP BY cust_id) AS t2
ON
t2.cust_id=x.cust_id
AND
t2.dd=x.order_date;