Używanie złączeń

Wprowadzenie do Oracle SQL

Sara Billen

Curriculum Manager

Zbiór danych Chinook

Diagram ER pełnego zbioru danych Chinook

Łączenie danych z więcej niż jednej tabeli

Albumy Pearl Jam

Złączenia SQL

Rodzaje złączeń:

Inner Join
Outer Joins
Cross Joins
Self Joins

Inner join

SELECT Album.Title, Artist.Name
FROM Album INNER JOIN Artist
ON  Album.ArtistId = Artist.ArtistId

| Album.Title                     | Artist.Name   |
|---------------------------------|---------------|
| Black Sabbath                   | Black Sabbath |
| Black Sabbath Vol. 4 (Remaster) | Black Sabbath |
| The Cream Of Clapton            | Eric Clapton  |
| Unplugged                       | Eric Clapton  |
| ...                             | ...           |

Budowa inner join

Wybierz kolumny do wyświetlenia i podaj nazwy tabel
W klauzuli FROM wymień odpowiednie tabele rozdzielone INNER JOIN
Użyj ON, aby wskazać kolumnę złączenia

SELECT Album.Title, Artist.Name

FROM Album INNER JOIN Artist

ON Album.ArtistId = Artist.ArtistId

Dodaj inne potrzebne klauzule, np. WHERE, ORDER BY!

Inner join

SELECT Album.Title, Artist.Name
FROM Album INNER JOIN Artist
ON  Album.ArtistId = Artist.ArtistId
WHERE Artist.Name = 'Pearl Jam'

| Album.Title | Artist.Name |
|-------------|-------------|
| Pearl Jam   | Pearl Jam   |
| Riot Act    | Pearl Jam   |
| Ten         | Pearl Jam   |
| ...         | ...         |

`USING` zamiast `ON`

SELECT Album.Title, Artist.Name
FROM Album INNER JOIN Artist
ON  Album.ArtistId = Artist.ArtistId

to samo co

SELECT Album.Title, Artist.Name
FROM Album INNER JOIN Artist
USING (ArtistId)

Kolumny muszą mieć identyczne nazwy w obu tabelach
Nazwę kolumny należy ująć w nawiasy

Aliasy tabel

SELECT DISTINCT Customer.FirstName, Customer.LastName, 
                Employee.FirstName, Employee.LastName
FROM Customer INNER JOIN Employee
ON Customer.SupportRepID = Employee.EmployeeID

Z aliasami:

SELECT DISTINCT c.FirstName, c.LastName, e.FirstName, e.LastName
FROM Customer c INNER JOIN Employee e
ON c.SupportRepID = e.EmployeeID

Złączenie więcej niż dwóch tabel

Tabele Track, Album i Artist

SELECT t.Name AS Track, al.Title AS Album, ar.Name AS Artist
FROM 
    Track t INNER JOIN Album al USING (AlbumId)
    INNER JOIN Artist ar USING (ArtistId)

Złączenie więcej niż dwóch tabel

SELECT t.Name as Track, al.Title as Album, ar.Name as Artist
FROM 
    Track t INNER JOIN Album al USING (AlbumId)
    INNER JOIN Artist ar USING (ArtistId)

| Track              | Album                          | Artist      |
|--------------------|--------------------------------|-------------|
| The Legacy         | A Matter of Life and Death     | Iron Maiden |
| Lord of Light      | A Matter of Life and Death     | Iron Maiden |
| Out of the Shadows | A Matter of Life and Death     | Iron Maiden |
| ...                | ...                            | ...         |

Czas na ćwiczenia!

Wprowadzenie do Oracle SQL