UNION & UNION ALL

Introduction à SQL Server

John MacKintosh

Instructor

SELECT 
  album_id, 
  title, 
  artist_id 
FROM album 
WHERE artist_id IN (1, 3)

+------------+-------------------------+------------|
| album_id   | title                   | artist_id  |
|------------+-------------------------|------------|
| 1          | For Those About To Rock | 1          |
| 4          | Let There Be Rock       | 1          |
| 5          | Big Ones                | 3          |
+------------+----------+---------------------------+

SELECT 
  album_id, 
  title, 
  artist_id 
FROM album 
WHERE artist_id IN (1, 4, 5)

+------------+-------------------------+------------|
| album_id   | title                   | artist_id  |
|------------+-------------------------|------------|
| 1          | For Those About To Rock | 1          |
| 4          | Let There Be Rock       | 1          |
| 6          | Jagged Little Pill      | 4          |
| 7          | Facelift                | 5          |
+------------+-------------------------+------------+

Combinaison des résultats

SELECT 
  album_id, 
  title, 
  artist_id 
FROM album 
WHERE artist_id IN (1, 3)

UNION

SELECT 
  album_id, 
  title, 
  artist_id 
FROM album 
WHERE artist_id IN (1, 4, 5);

+------------+-------------------------+------------|
| album_id   | title                   | artist_id  |
|------------+-------------------------|------------|
| 1          | For Those About To Rock | 1          |
| 4          | Let There Be Rock       | 1          |
| 5          | Big Ones                | 3          |
| 6          | Jagged Little Pill      | 4          |
| 7          | Facelift                | 5          |
+------------+-------------------------+------------+

Les lignes en double sont exclues

UNION ALL

SELECT 
  album_id, 
  title, 
  artist_id 
FROM album 
WHERE artist_id IN (1, 3) 
UNION ALL 
SELECT 
  album_id, 
  title, 
  artist_id 
FROM album 
WHERE artist_id IN (1, 4, 5);

+------------+-------------------------+------------|
| album_id   | title                   | artist_id  |
|------------+-------------------------|------------|
| 1          | For Those About To Rock | 1          |
| 4          | Let There Be Rock       | 1          |
| 5          | Big Ones                | 3          |
| 1          | For Those About To Rock | 1          |
| 4          | Let There Be Rock       | 1          |
| 6          | Jagged Little Pill      | 4          |
| 7          | Facelift                | 5          |
+------------+-------------------------+------------+

Inclut les lignes en double

Création de nouveaux noms de colonnes pour les résultats finaux

SELECT 
  album_id AS ALBUM_ID, 
  title AS ALBUM_TITLE, 
  artist_id AS ARTIST_ID 
FROM album 
WHERE artist_id IN(1, 3) 
UNION ALL 
SELECT 
  album_id AS ALBUM_ID, 
  title AS ALBUM_TITLE, 
  artist_id AS ARTIST_ID 
FROM album 
WHERE artist_id IN(1, 4, 5)

+------------+-------------------------+------------|
| ALBUM_ID   | ALBUM_TITLE             | ARTIST_ID  |
|------------+-------------------------|------------|
| 1          | For Those About To Rock | 1          |
| 4          | Let There Be Rock       | 1          |
| 5          | Big Ones                | 3          |
| 1          | For Those About To Rock | 1          |
| 4          | Let There Be Rock       | 1          |
| 6          | Jagged Little Pill      | 4          |
| 7          | Facelift                | 5          |
+------------+-------------------------+------------+

Récapitulatif

UNION ou UNION ALL : Combine les requêtes provenant de la même table ou de tables différentes

Si vous combinez des données provenant de différentes tables :

Sélectionner le même nombre de colonnes dans le même ordre
Les colonnes doivent contenir les mêmes types de données

Si les tables sources ont des noms de colonnes différents

Créer des alias de noms de colonnes

UNION : Supprime les doublons (exécution plus lente)

UNION ALL : Inclut les doublons (exécution plus rapide)

Passons à la pratique !

Introduction à SQL Server