SQL JOIN語法 產品銷售分析 I Leetcode #1068

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題目敘述

題目會給我們兩張資料表，第一張是Sales，第二張是Product。

第一張是Sales表格，裡面分別有sale_id、 product_id、year、quantity、price等欄位。其中(sale_id、 product_id)做為複合主鍵Primary key

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.

第二張是Product表格，裡面分別有product_id 、 product_name 等欄位。其中 product_id做為主鍵Primary key

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.

要求我們列出每一項銷售產品的 產品名稱product_name、銷售年分year、銷售價格price

輸出的順序不拘。

詳細的題目可在這裡看到

測試範例

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_name | year  | price |
+--------------+-------+-------+
| Nokia        | 2008  | 5000  |
| Nokia        | 2009  | 5000  |
| Apple        | 2011  | 9000  |
+--------------+-------+-------+
Explanation: 
From sale_id = 1, we can conclude that Nokia was sold for 5000 in the year 2008.
From sale_id = 2, we can conclude that Nokia was sold for 5000 in the year 2009.
From sale_id = 7, we can conclude that Apple was sold for 9000 in the year 2011.

演算法

考點主要在考怎麼串聯兩張表格? 用兩張表格共有的product_id欄位做連接，並且依照提議印出產品名稱product_name、銷售年分year、銷售價格price。

對應的SQL語法

SELECT ...欄位

FROM ...第一張表格

JOIN ...第二張表格 USING(共同欄位)

或者

SELECT ...欄位

FROM ...第一張表格

JOIN ...第二張表格

ON ...連接條件

程式碼

SELECT P.product_name, S.year, S.price
FROM Sales S
LEFT JOIN Product P USING(product_id);

SELECT P.product_name, S.year, S.price
FROM Sales S
LEFT JOIN Product P 
ON P.product_id=S.product_id;

關鍵知識點

掌握JOIN 的SQL語法 搭配連接條件判斷的用法

SELECT ...欄位

FROM ...第一張表格

JOIN ...第二張表格 USING(共同欄位)

或者

SELECT ...欄位

FROM ...第一張表格

JOIN ...第二張表格

ON ...連接條件

Reference:

[1] MySQL by LEFT JOIN ... USING(common key) - Product Sales Analysis I - LeetCode