成本與共通資料表表示式（CTE）

使用 SQL 分析商業資料

Michel Semaan

Data Scientist

成本

公司支出的金額
範例
- 員工薪資
- 車隊購置與維護
- 餐點成本

你需要的資料表

meals

meal_id   eatery                    meal_price  meal_cost
--------  ------------------------  ----------  ---------
0         'Leaning Tower of Pizza'  4           2         
1         'Leaning Tower of Pizza'  3.5         1.25      
2         'Leaning Tower of Pizza'  4.5         1.75
...       ...                         ...         ...

stock

stocking_date  meal_id   stocked_quantity
-------------  --------  ----------------
2018-06-01     0         76               
2018-06-01     1         42               
2018-06-01     2         56
...            ...       ...

計算成本

查詢

SELECT
  meals.meal_id, 
  SUM(meal_cost * stocked_quantity) AS cost 
FROM meals
JOIN stock ON meals.meal_id = stock.meal_id
GROUP BY meals.meal_id
ORDER BY meals.cost DESC
LIMIT 3;

結果

meal_id  cost      
  --------
9        3820.0
7        3592.5    
8        2332.5

如何合併收入與成本？

利潤 = 收入 - 成本
已撰寫收入與成本的個別查詢

共通資料表表示式（CTE）

將查詢結果存成暫存表
在後續查詢引用該暫存表

查詢

WITH table_1 AS
  (SELECT ...
   FROM ...),
  table_2 AS
  (SELECT ...
   FROM   ...)

SELECT ...
FROM table_1
JOIN table_2 ON ...
...

CTE 實作

查詢

WITH costs_and_quantities AS (
 SELECT
   meals.meal_id,
   SUM(stocked_quantity) AS quantity,
   SUM(meal_cost * stocked_quantity) AS cost
 FROM meals
 JOIN stock ON meals.meal_id = stock.meal_id
 GROUP BY meals.meal_id)


SELECT 
  meal_id,
  quantity,
  cost
FROM costs_and_quantities
ORDER BY cost DESC
LIMIT 3;

結果

meal_id  quantity  cost      
-------  --------  -------
5        3062      12248     
4        3142      10211.5   
6        2989      8219.75

成本與共通資料表表示式（CTE）

使用 SQL 分析商業資料