关于表连接（join(inner join),left join(left outer join)）

1、准备工作并插入数据：

创建两张表：student和class

CREATE TABLE CLASS

(

ID INT PRIMARY KEY,

NAME VARCHAR2(50)

);

CREATE TABLE STUDENT

(

STUNO INT PRIMARY KEY ,

STUNAME VARCHAR2(50),

CLASS_ID INT,

CONSTRAINT FK_STU_CLASS FOREIGN KEY (CLASS_ID)

REFERENCES CLASS(ID)

);

查询表情况如下：


使用左连接的的SQL语句：

SELECT C.ID CLASS_ID,C.NAME CLASS_NAME,S.STUNAME STUDENT_NAME FROM CLASS C LEFT JOIN STUDENT S ON C.ID=S.CLASS_ID;

使用内连接的SQL语句：

SELECT C.ID CLASS_ID,C.NAME CLASS_NAME,S.STUNAME STUDENT_NAME FROM CLASS C JOIN STUDENT S ON C.ID=S.CLASS_ID;

执行后的结果如下图：