Oracle 基础学习记录 (keep updating)

keyword: 笛卡尔集Cartesian

写成xx.xx是为了性能

1. Select table1.column Select table2.column

FROM table1,table2

WHERE table1.column1 = table2.column2

2. Equal Join

Table 1 :EMPLOYEE

EMPLOYEE_ID DEPARTMENT_ID

200 10

201 20

202 30

DEPARTMENT_ID 是 Foreign Key

Table 2:DEPARTMENT

DEPARTMENT_ID DEPARTMENT_NAME

10 Admin

20 Market

30 IT

DEPARTMENT_ID 是主键

SELECT employees.employee_id,employees.last_name,
employees.department_id,departments.department_id,
departments.location_id
FROM employees,departments
WHERE employees.department_id = departments.departmetn_id;