撰寫可讀性高的程式碼

將 SQL 應用於真實世界問題

Dmitriy (Dima) Gorenshteyn

Lead Data Scientist, Memorial Sloan Kettering Cancer Center

SQL 關鍵字大寫

原始版本

select 
  title as film_title, 
  description as film_description
from rental as r
join inventory as i
  on r.inventory_id = i.inventory_id
join film as f
  on i.film_id = f.film_id
where f.length > 90
  and f.replacement_cost > 20;

改良版本

SELECT 
  title AS film_title, 
  description AS film_description
FROM rental AS r
JOIN inventory AS i
  ON r.inventory_id = i.inventory_id
JOIN film AS f
  ON i.film_id = f.film_id
WHERE f.length > 90
  AND f.replacement_cost > 20;

使用換行與縮排

原始版本

SELECT title, description
FROM rental AS r
JOIN inventory AS i
ON r.inventory_id = i.inventory_id
JOIN film AS f ON i.film_id = f.film_id
WHERE f.length > 90 AND f.replacement_cost > 20;

改良版本

SELECT title, 
       description 
FROM rental AS r
JOIN inventory AS i
  ON r.inventory_id = i.inventory_id
JOIN film AS f
  ON i.film_id = f.film_id
WHERE f.length > 90
  AND f.replacement_cost > 20;

使用 snake_case

原始版本

SELECT 
  title expensivelongtitle, 
  description expensivelongdescription
FROM rental AS r
...

改良版本

SELECT 
  title expensive_long_title, 
  description expensive_long_description
FROM rental AS r
...

用 IN 取代多個 OR 條件

原始版本

SELECT 
    address_id,  
    district 
FROM address
WHERE district = 'Texas'
  OR district = 'Bihar'
  OR district = 'Chiba'
  OR district = 'Chiayi'
  OR district = 'Gois';

改良版本

SELECT 
    address_id,  
    district 
FROM address
WHERE district IN ('Texas', 'Bihar', 'Chiba', 
                   'Chiayi', 'Gois');

能用 BETWEEN 就用 BETWEEN

原始版本

SELECT 
  title, 
  description
FROM film
WHERE replacement_cost > 15
  AND replacement_cost < 25;

改良版本

SELECT 
  title, 
  description
FROM film
WHERE replacement_cost BETWEEN 15 AND 25;

一起來練習吧！

將 SQL 應用於真實世界問題