Éviter les erreurs courantes

Appliquer SQL à des problèmes réels

Dmitriy (Dima) Gorenshteyn

Lead Data Scientist, Memorial Sloan Kettering Cancer Center

N'abusez pas des commentaires

/* When selecting category and length
from films we need to use f, after this
I had a sandwich, it was a 
good sandwich ...*/
SELECT category, length
-- FROM actor as a
FROM film AS f
/* Inner join the table category 
with the film table */
INNER JOIN category AS c
ON f.film_id = c.film_id;

À éviter

Rédiger un roman dans vos commentaires.

N'abusez pas des commentaires





SELECT category, length
-- FROM actor as a
FROM film AS f
/* Inner join the table category 
with the film table */
INNER JOIN category AS c
ON f.film_id = c.film_id;

À éviter

Rédiger un roman dans vos commentaires.
Laisser de vieux commentaires dans du code final.

N'abusez pas des commentaires





SELECT category, length

FROM film AS f
/* Inner join the table category 
with the film table */
INNER JOIN category AS c
ON f.film_id = c.film_id;

À éviter

Rédiger un roman dans vos commentaires.
Laisser de vieux commentaires dans du code final.
Ajouter des commentaires redondants avec le code.

N'abusez pas des commentaires

/* When selecting category and length
from films we need to use f, after this
I had a sandwich, it was a 
good sandwich ...*/
SELECT category, length
-- FROM actor as a
FROM film AS f
/* Inner join the table category 
with the film table */
INNER JOIN category AS c
ON f.film_id = c.film_id;

SELECT category, length
FROM film AS f
INNER JOIN category AS c
ON f.film_id = c.film_id;

N'utilisez pas SELECT *

SELECT *
FROM film AS f
INNER JOIN category AS c
ON f.film_id = c.film_id;

release_year language_id rental_duration rental_rate length  .......
2009            1            4              6.99        173  .......    
2006            1            7              6.99        185  .......    
2004            1            5              4.99        153  .......    
2007            1            7              2.99        69   .......

N'utilisez pas SQL pour programmer

DO $$
BEGIN
   FOR counter IN 1..5 LOOP
     IF (counter = 2) THEN
      RAISE NOTICE 'BINGO!';
     ELSE 
      RAISE NOTICE 'Not BINGO :-(';
     END IF;
   END LOOP;
END; $$

NOTICE:  1 Not BINGO :-(
NOTICE:  1 BINGO!
NOTICE:  3 Not BINGO :-(
NOTICE:  4 Not BINGO :-(
NOTICE:  5 Not BINGO :-(

Passons à la pratique !

Appliquer SQL à des problèmes réels