编写可读代码

将 SQL 应用于真实问题

Dmitriy (Dima) Gorenshteyn

Lead Data Scientist, Memorial Sloan Kettering Cancer Center

SQL 关键字大写

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;

改进版本

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;

使用换行与缩进

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;

改进版本

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
...

改进版本

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

用 IN 替代多个 OR

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';

改进版本

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

尽量使用 BETWEEN

原始版本

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

改进版本

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

¡Vamos a practicar!

将 SQL 应用于真实问题