使用连接

Oracle SQL 入门

Sara Billen

Curriculum Manager

Chinook 数据集

Chinook 数据集 ER 图

合并多表数据

Pearl Jam 专辑

SQL 连接

连接类型：

内连接（Inner Join）
外连接（Outer Joins）
交叉连接（Cross Joins）
自连接（Self Joins）

内连接（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  |
| ...                             | ...           |

内连接步骤解析

选择输出列并包含表名
在 FROM 中，用 INNER JOIN 分隔列出相关表
用 ON 指定连接列

SELECT Album.Title, Artist.Name

FROM Album INNER JOIN Artist

ON Album.ArtistId = Artist.ArtistId

再添加 WHERE、ORDER BY 等必要子句！

内连接（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   |
| ...         | ...         |

用 USING 替代 ON

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

等同于

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

两表中列名必须完全相同
将列名放在圆括号中

表别名

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

使用别名：

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

连接两张以上的表

曲目、专辑和艺术家表

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)

连接两张以上的表

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 |
| ...                | ...                            | ...         |

Passons à la pratique !

Oracle SQL 入门