9/2 每日一題MYSQL(尋找產品第一次上市的資料)

Table: Sales

+-------------+-------+
| Column Name | Type  |
+-------------+-------+
| sale_id     | int   |
| product_id  | int   |
| year        | int   |
| quantity    | int   |
| price       | int   |
+-------------+-------+
(sale_id, year) is the primary key (combination of columns with unique values) of this table.
product_id is a foreign key (reference column) to Product table.
Each row of this table shows a sale on the product product_id in a certain year.
Note that the price is per unit.

 

Table: Product

+--------------+---------+
| Column Name  | Type    |
+--------------+---------+
| product_id   | int     |
| product_name | varchar |
+--------------+---------+
product_id is the primary key (column with unique values) of this table.
Each row of this table indicates the product name of each product.

 

Write a solution to select the product id, year, quantity, and price for the first year of every product sold.

Return the resulting table in any order.

The result format is in the following example.

 

Example 1:

Input: 
Sales table:
+---------+------------+------+----------+-------+
| sale_id | product_id | year | quantity | price |
+---------+------------+------+----------+-------+ 
| 1       | 100        | 2008 | 10       | 5000  |
| 2       | 100        | 2009 | 12       | 5000  |
| 7       | 200        | 2011 | 15       | 9000  |
+---------+------------+------+----------+-------+
Product table:
+------------+--------------+
| product_id | product_name |
+------------+--------------+
| 100        | Nokia        |
| 200        | Apple        |
| 300        | Samsung      |
+------------+--------------+
Output: 
+------------+------------+----------+-------+
| product_id | first_year | quantity | price |
+------------+------------+----------+-------+ 
| 100        | 2008       | 10       | 5000  |
| 200        | 2011       | 15       | 9000  |
+------------+------------+----------+-------+

 # Write your MySQL query statement below

SELECT S.product_id, S.year AS first_year ,S.quantity ,S.price

FROM Sales AS S

WHERE (S.product_id,S.year) IN (SELECT product_id,MIN(year) FROM Sales GROUP BY product_id)

#--子查詢選擇product_id的最小year 和 product_id

#主產尋中 查詢 product_id,year, quantity ,price

從Sales表中

其中product_id, year 要符合子查詢中的 product_id 的最小 year 組合匹配