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実世界の課題にSQLを適用する

Dmitriy (Dima) Gorenshteyn

Lead Data Scientist, Memorial Sloan Kettering Cancer Center

SQL コマンドは大文字にする

元の例

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;

改善例

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;

改行とインデントを使う

元の例

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;

改善例

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;

snake_case を使う

元の例

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

改善例

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

OR を並べる代わりに IN を使う

元の例

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

改善例

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

可能なら BETWEEN を使う

元の例

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

改善例

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

Ayo berlatih!

実世界の課題にSQLを適用する